//^  -    y^f 


SOIL  SURVEY  OF  I.OWA 

POTTAWATTAMIE  COUNTY  SOILS 


AGRICULTURAL  EXPERIMENT  STATION 

IOWA  STATE  COLLEGE  OF  AGRICULTURE 

AND  MECHANIC  ARTS 


Agfonomy  Section 
Soils 


Soil  Survey  Report  No.  2 

January,  1918 

Ames,  Iowa 


OFFICERS  AND  STAFF 
IOWA  AGRICULTURAL  EXPERIMENT  STATION 

Raymond  A.  Pearson,  M.  S.  A.,  LL.  D.,  President 

C.   P.   Curtiss,   M.   S.   A.,   D.   S.,   Director 

W.  H.  Stevenson,  A.  B.,  B.  S.  A.,  Vice-Du-ector 

AGRICULTURAL  ENGINEERING 
C.  K.  Shedd,  B.  S.  A.,  B.  S.  in  A.  E.,  Acting  Chief  W.  A.  Foster,  B.  S.  in  Ed.,  B.  Arch.,  Assistant 

J.  S.  Glass,  B.  S.  in  A.  E.,  Assistant 

AGRONOMY 

W.  H.  Stevenson,  A.  B.,  B.  S.  A.,  Chief  H.   W.   Johnson,   B.   S.,   M.   S.,  Assi.stant  in   Soils 
H.   D.   Hughes,   B.    S.,   M.    S.   A.,   Chief   in   Farm  (absent  on  leave) 

Crops  George  E.  Corson,  B.  S.,  M.  S.,  Assistant  in  Soil 
P.  E.  Brown,  B.  S.,  A.  M.,  Ph.  D.,  Cliief  in  Soil  Survey 

Chemistrj'  and  Bacteriologj-.  H.   W.   Warner,   B.   S.,   M.   S.,   Soil   Survieyor    (ab- 
L.   C.   Burnett,   B.   S.   A.,   M.   S.,   Cliief   in   Cereal  sent  on  leave) 

Breeding  L.    L.    Rhodes,    B.    S.,    Soil    Survey     (absent    on 
L.  W.  Forman,  B.  S.  A.,  M.  S.,  Chief  in  Field  Ex-  leave) 

perinients  M.  E.   Olson,   B.   S.,   M.   S.,  Field  Experiments 

John   Buchanan,   B.   S.  A.,   Superintendent  of  Co-  J.  F.  Bisig,  B.  8.,  Field  Experiments 

operative  Experiments  O.    F.    Jensen,    B.    S.,    M.    S.,   Assistant    in    Farm 
R.  S.  Potter,  A.  B.,  M.  S.,  Ph.  D.,  Assistant  Chief  Crops  (absent  on  leave) 

in  Soil  Chemistry-  E.  I.  Angell,  Soil  Surveyor 

R.  S.  Snyder,  B.  S.,  Assistant  in  Soil  Chemistry  H.   P.  Hanson,   B.   S.,   Field  Experiments    (absent 

on  leave) 

ANIMAL   HUSBANDRY 
W.  H.  Pew,  B.  S.  A.,  Chief  L.    S.    Gillette,    B.    S.,    M.    S.,    Assistant   Chief    in 

J.   M.   Eward,   M.    S.,   Assistant   Chief   in   Animal  Dairy  Husbandry 

Husbandry  and  Chief  in  Swine  Production  A.   C.   McCandJish,    M.    S. -A.,   Assistant  in    Dairy 

R.  Dunn,  B.  S.,  Assistant  in  Animal  Husbandry  Husbandrj- 

Orren    Lloyd-Jones,    M.    S.,    Ph.    D.,    Assistant    in  Rodney  Miller,  B.  S.  A.,  Assistant  in  Poultrj-  Hus- 

Animal  Husbandry  bandry. 

H.    A.    Bittenbender,    B.    S.    A.,    Chief    in    Poultry 

Husbandry 

BACTERIOLOGY 
R.  E.  Buchanan,  M.  S.,  Ph.  D.,  Chief;  Associate  in  Daii"y  and  Soil  Bacteriology 

BOTANY 
L.  H.  Pammel,  B.  Agr.,   M.  S.,  Ph.  D.,  Chief  I.  E.  Melhus,  B.  S.,  Ph.  D.,  Chief  in  Plant  Path- 

Charlotte  M.  King,  Assistant  Cliief  ology' 

CHEMISTRY 

A.  W.   Dox,   B.   S.  A.,   A.   M.,   Ph.   D.,   Chief    (on  A.  R.  Lamb,  B.  S.,  M.  S.,  Assistant 

leave  of  absence)  S.  B.  Kuzirian,  A.  B.,  A.  M.,   Ph.  1).,  Assistant 

W.  G.  Gaessler,  B.  S.,  Acting  Chief  G.  W.  Roark,  Jr.,  B.  S.,  Assistant 

Lester  Yoder,  B.  S.,  M.  S.,  Assistant 

DAIRYING 
M.  Mortensen,  B.  S.  A.,  Chief  I).  E.  Bailey,  M.  S.,  Assistant  Chief  in  Dairying 

B.  W.   Hammer,   B.    S.   A.,    Chief   in    Dairy    Bac- 
teriology 

ENTOMOLOGY 
R.  L.  Webster,  A.  B.,  Chief  Wallace   Park,  B.  S.,  Assistant  in   Apiculture 

FARM  MANAGEMENT 
H.  B.  Munger,  B.  S.,  Chief  O.  G.  Lloyd,  B.  S.,  M.  S.,  Assistant  Chief 

HORTICULTURE  AND  FORESTRY 
S.  A.  Beach,  B.  S.  A.,  M.  S.,  Cliief  A.  T.  Erwin,  M.  S.,  Chief  in  Truck  Crops 

T.  J.  Maney,  B.  S.,  Chief  in  Pomology  Rudolph  A.   Rudnick,    B.    S.,    Assistant  in   Truck 

Harvey  L.  Lantz,  B.  S.,  Assistant  in  Fruit  Breed-  Crops 

ing  G.  B.  MacDonald,  B.  S.  F.,  M.  F.,  Chief  in  For- 

W.  E.  Whitehouse,  B.  S.,  Assistant  in  Pomology  estry 

Ajidrew  Edward  Mumeck,  B.  A.,  Research  Fellow  Frank  H.  Culley,  B.  S.,  M.  L.  A.,  Chief  in  Land- 

in  Pomology  scape  Architecture 

J.  B.  Kendrick,  B.  A.,  Research  Assistant  in  Pom- 
ology 

RURAL  SOCIOLOGY 
G.  H.  Von  Tungeln,  Ph.  B.,  M.  A.,   Chief 

VETERINARY  MEDICINE 
C.  H.   Stange,   D.  V.  M.,   Chief 

GENERAL  OFFICERS 
F.  W.  Beckman,  Ph.  B.,  Bulletin  Editor  F.  E.  Colbum,   Photographer 

Gretta    Smith,    A.    B.,    Assistant    to    the    Bulletin  C.  E.  Brashear,  B.  S.  A.,  Assistant  to  Director 

Editor 


SRLF     QO 
URL 


/44^'V^'^' 


CONTEXTS 

Introduction    5 

Pottawattamie   county's  fann   crops 6 

Pottawattamie  county's  live  stock  iiidu^tiy 7 

Geologry  of  Pottawattamie  counl >■ 8 

Physiography  and   drainage 9 

Soils  of  Pottawattamie  county 11 

The  different  types  and  their  areas 11 

The  fertility  in  Pottawattamie  county  soils 12 

The  surface   soils 12 

The  subsurface  soils  and  s\ibsoils 15 

Greenhouse  experiments 16 

Field   experiment 19 

Field  experiments  with  gumbo 22 

Needs  of  Pottawattamie  county  soils  as  indicated  by  clKMiiieaK  greenhouse  and 

field  tests " " 24 

Manuring    24 

Commercial    fertilizers 26 

Lime 27 

Drainage 28 

Rotation  of  crops 28 

Prevention  of  erosion 29 

Dead   furrows 30 

Small    gullies 30 

Large   gidlies 33 

Bottomlands    33 

Hillside  erosion 33 

Individual  soil  types  in  Pottawattamie  enuiity 34 

Loess   soils 34 

Tei-raee  soils 36 

Swamp  and   bottoiidand  soils 39 

Appendix  :     The  soil  survey  of  Towa 45 


POTTAWATTAMIE  COUNTY  SOILS 

By  W.  H.  Stevenson,  P.  E.  Brown,  with  the  assistance  of  II.  P.  Hanson  and 

H.  W.  Reid 

Pottawattamie  county  is  located  in  southwestern  Iowa  along  the  Missouri  river. 
It  is  the  second  largest  county  in  the  state,  having  a  total  area  of  957  square 
miles,  or  612,480  acres.  It  is  entirely  wuthin  the  Missouri  loess  soil  area;  70% 
of  its  soils  being  loessial  in  origin,  while  the  remaining  types  fall  within  the  ter- 
race and  swamp  and  bottomland  groups. 

This  county  is  one  of  the  most  important  in  the  state  agriculturally,  not  alone 
because  of  its  size,  but  also  because  of  the  high  normal  fertility  of  its  soils  and  the 
wonderful  adaptation  of  soil  and  climatic  conditions  to  the  growth  of  certain 
valuable  crops. 

Of  the  total  area  of  Pottawattamie  county,  518,784  acres,  or  84.7%  is  in  farms 
numbering  3,101  in  all  with  an  average  size  per  farm  of  167  acres. 

The  utilization  of  the  farm  land  is  indicated  by  the  folloAving  figures,  compiled 
by  the  state  department  of  agriculture  in  1915 : 

Acreage  in  pasture 131,000  acres 

Acreage  in  farm  buildings,  feed  lots  and  public  highways. . . .  24,639  acres 

Acreage  in  orchards 4,962  acres 

Acreage  in  gardens : 1,106  acres 

Acreage  in  waste  land 4,559  acres 

Acreage  in  general  farm  crops 356,050  acres 

Acreage  in  crops  not  otherwise  listed 745  acres 

The  type  of  agriculture  is  indicated  rather  definitely  in  the  figures  just  given 
and  consists  in  general  farming  combined  to  a  considerable  extent  with  live- 
stock raising.  The  acreage  in  orchards  is  not  large,  but  fruit  growing  is  in- 
creasing rapidly  in  the  county.  With  the  infomiation  which  is  now  being  se- 
cured and  disseminated  regarding  the  growing  and  marketing  of  fruits,  or- 
charding will  undoubtedly  become  of  much  importance.*  Systems  of  perma- 
nent fertility  adapted  to  Pottawattamie  county  should,  therefore,  include  not 
only  general  farming,  and  live  stock  farming,  but  also  orcharding. 

The  area  of  waste  land  in  this  county  is  not  great  but  it  warrants  attention 
and  methods  of  reclamation  or  utilization  should  be  devised.  Definite  advice 
along  this  line,  of  course,  can  only  be  given  for  individual  conditions  and  no 
general  recommendations  can  be  made  here. 

*  See  Soil  Survey  of  Pottawattamie  County,  Towa.  by  A.  L.  Goodman  of  the  U.  S.  Depart- 
ment of  Agriculture,  and  Peter  Hanson  and  Harold  W.  Eeid  of  the  Iowa  Agricultural  Ex- 
periment Station. 

*  An  experiment  orchard  maintained  by  the  Iowa  Agricultural  Experiment  Station  near 
Council  Bluffs  is  yielding  much  information  of  value  to  fruit  growers  of  Pottawattamie  and 
adjoining  counties. 


6  SOIL  SUEVEY  OF  IOWA 

TABLE  I.     ACREAGE,  YIELDS  AND  VALUES  OF  FARM  CROPS  IN  POTTAWATTA- 
MIE COUNTY* 


Acres 


So  total  farm  jBu.  or  tons  j  Total  bushels 
land  incountrl    per  acre    |       or  tons 


Average 
price 


Total 
value  crop 


Corn     194,000 


Oats 

Spring    wheat . 

Winter  wheat.  . 

Barley 

Rye    

Potatoes   

Tame    hay.  . .  . 

Wild   hay. 

Alfalfa    


43,900 
10,900 
32,000 

5,800 
500 

1,850 
34,900 

9.700 
22,500 
Pasture |     131,000 


6,402,000 

1,404,800 

163,500 

640,000 

162,400 

10,000 

140,600 

59,300 

14,500 

81,000 


0.45 
0.32 
0.85 
0.83 
0.51 
0.77 
0.53 
8.94 
7.41 
11.18 


$2,880,900 
449,536 
138,975 
531,200 

82,824 
7,700 

74,518 
530,1.42 
107,445 
905,580 


Over  three-fifths  of  the  farm  land  is  employed  for  general  farming  and  the 
crops  grown,  in  the  order  of  their  importance,  are  com,  alfalfa,  winter  wheat, 
tame  har,  oats,  spring  wheat,  wild  hay,  barley,  potatoes,  and  rA'e. 

POTTAWATTAMIE  COUNTY'S  FARM  CROPS 

Corn  is  particularly  adapted  to  Pottawattamie  county  and  does  well  on  all  the 
soil  types,  but  it  is  especially  suited  to  the  Marshall  silt  loam  where  the  yields 
are  generally  high.  On  the  terrace  and  swamp  and  bottomland  soils  yields  are 
usually  lower  than  on  the  upland  soils,  but  in  favorable  seasons  quite  satisfac- 
tory crops  are  obtained.  The  value  of  the  corn  crop  is  verj^  much  greater  than 
that  of  any  of  the  other  crops  grown,  as  will  be  seen  in  table  I. 

The  ^Missouri  loess  soil  area  as  a  whole  is  especially  suited  to  the  growth  of 
alfalfa  and  Pottawattamie  county  stands  second  among  all  the  counties  of  Iowa 
in  the  production  of  this  crop.  Alfalfa  grows  well  on  all  the  soil  tjT)es  in  the 
county  but  like  com,  it  does  especially  well. on  the  Marshall  silt  loam.  Very 
few  failures  to  secure  satisfactory  yields  are  recorded  and  three  or  four  cuttings 
are  usually  made  with  jaelds  up  to  seven  tons  per  acre  as  a  common  occurrence. 
The  value  of  alfalfa  in  this  county  is  second  only  to  com  and  the  acreage  is  in- 
creasing each  year.  Sweet  clover  is  being  grown  to  some  extent  in  place  of  al- 
falfa, but  its  use  is  not  general  and  it  is  doubtful  if  it  will  ever  prove  as  val- 
uable as  a  forage  crop. 

The  next  crop  of  importance  in  this  county  is  wheat.  Both  winter  wheat  and 
spring  wheat  have  been  grown,  but  spring  wheat  has  been  quite  generally  re- 
placed by  the  more  profitable  "v^-inter  variety.  At  the  present  time  the  acreage 
of  the  latter  is  three  times  that  of  the  former.  The  average  yield  of  the  -sAinter 
wheat  is  greater  than  that  of  the  spring  variety  and  the  total  value  to  the  coun- 
ty is,  therefore,  much  greater. 

The  tame  hay  crop  in  Pottawattamie  count}'  far  exceeds  the  wild  hay  in  acre- 
age, yield  and  value.  The  tame  hay  is  made  up  practically  entirely  of  timothy 
and  red  clover  and  its  value  alone  exceeds  that  of  the  grain  crops,  except  com 
and  wheat. 

Oats  stand  next  to  corn  in  acreage  and  production,  but  its  value  is  less  than 
that  of  alfalfa,  wheat,  and  hay.     It  is  a  verj-  important  crop  and  is  found  in 


*  Iowa  Year  Book  of  Agriculture,  1915. 


POTTAWATTAMIE  COUNTY  SOILS  7 

nearly  all  rotations,  satisfactory  yields  being  secured  in  most  cases.  Practically 
all  the  oats  produced  in  Pottawattamie  county  is  fed  on  the  farms. 

Barley,  rye,  and  potatoes  are  gro^\Ti  to  some  extent,  but  the  acreage  is  not 
large  and  their  value  is  much  less  than  tliat  of  the  crops  already  mentioned. 

The  suitability  of  the  land  along  the  ^Missouri  river  to  the  production  of  apples 
and  grapes  was  recognized  by  the  early  settlers.  It  is  only  within  recent  years, 
however,  that  these  crops  have  been  grown  to  any  considerable  extent.  The 
yield  of  apples  in  the  county  in  1915  was  81,942  bushels  and  the  production  is 
constantly  increasing.  The  varieties  grown  are  Ben  Davis,  Roman  Stem,  Grimes 
Golden,  Gano,.  Jonathan,  Winasap,  Mammoth  Black  Twig,  and  Northwestern 
Greening.  Grape  growing  has  also  increa.sed  considerably.  Over  600  acres  are 
now  in  vineyards  and  the  yields  and  profits  are  quite  satisfactory.  The  dis- 
posal of  the  crop  is  much  facilitated  thru  the  aid  of  cooperative  buying  and  sell- 
ing associations.  Grapes  are  particularly  suited  to  the  Knox  silt  loam  and 
prove  valuable  on  the  steep  blutf  land  near  the  Missouri  river  where  field  crops 
cannot  be  gro^^^l  satisfactorily.  Better  methods  of  handling  the  \nneyards  are 
quite  necessary  in  many  cases  and  if  proper  treatment  of  the  soil  and  vines  is 
followed,  this  crop  can  be  made  one  of  the  most  profitable  in  the  county. 

POTTAWATTAMIE  COUNTY  LIVE  STOCK  INT)USTRY 

The  livestock  industrj-  is  well  developed  in  Pottawattamie  county.  Good 
market  facilities  and  excellent  blue  grass  pastures  render  it  one  of  the  leading 
stock  raising  counties  in  the  state. 

The  extent  of  this  industry  is  indicated  in  the  following  figures  compiled  in 

1915:  ^,  ^_.^ 

Horses  (all  ages) 21, /0.5 

Mules  (all  ages) 2,610 

Swine  (July  1.  1915) 195,496 

Cattle  (cows  and  heifers  kept  for  milk) ....  12,874 

Cattle  (other  cattle  not  kept  for  milk) 52,743 

Cattle  (total,  all  ages) 71,970 

Sheep  (all  ages  on  farms) 5,627 

Sheep  (shipped  in  for  feeding) 7,007 

Sheep  (total  pounds  wool  clipped) 34,916 

The  livestock  industry'  is  profitable  and  should  undoubtedly  be  developed  to  a 
much  greater  extent.  Not  only  are  there  good  returns  on  the  investment  made, 
but  the  drain  on  the  natural  fertility  of  the  soil  is  less  under  livestock  farming. 

The  value  of  land  in  Pottawattamie  county  is  extremely  variable.  The  bot- 
tom lands  along  the  Missouri  river,  the  least  valuable  because  they  are  subject 
to  overflow,  sell  for  $65  to  $100  per  acre.  They  produce  good  crops  in  favor- 
able seasons.  In  the  eastern  three-fourths  of  the  county,  where  the  land  is 
gently  rolling  to  hilly,  the  prices  range  from  $125  to  $250  per  acre  and  here  soil 
and  climatic  conditions  are  favorable  for  the  very  best  crop  production. 

Yields  of  all  crops  in  Pottawattamie  county  are  good,  but  experiments  show 
ver}'  definitely  that  they  may  be  increased  thru  proper  methods  of  management. 
The  soils  are  not  acid  except  in  a  few  eases  and  do  not  generally  need  lime. 
Thev  are  low  in  organic  matter  or  humus,  however,  and  care  should  be  taken  to 


SOIL  SURVEY  OF  IOWA 


Fig.   1.     Rich  alluvial  soil  on  the  Missouri  river  bottoms.     Cliaraeteristic  loess  bluffs  in  the 
distance.     The  alluvial  soils  are  classified  in  the  Wabash  soils 

provide  enough  of  this  important  material.  "With  proper  treatment  and  crop- 
ping, the  yields  from  the  soils  in  this  county  may  be  increased  to  a  considerable 
extent. 

THE  GEOLOGY  OF  POTTAWATTAMIE  COUNTY 

Pottawattamie  county  is  located  in  the  midst  of  the  Missouri  loess  soil  area 
bordering  on  the  Missouri  river.  About  three-fourths  of  the  county  consists  of 
level  to  hilly  loessial  upland  and  the  remaining  portion  is  made  up  of  flat  to 
gently  undulating  alluvial  plains  or  first  bottoms. 

The  rock  material  underlying  the  soils  of  Pottawattamie  county  represents 
various  geological  eras  and  is  of  interest  technically,  but  from  the  agricultural 
standpoint  it  is  of  no  importance  for  it  is  so  deep  under  the  overlying  loess  that 
it  can  have  practically  no  effect  on  the  growth  of  crops. 

The  whole  county  was  covered  by  at  least  one  glacier  in  times  past,  for  evi- 
dences of  glacial  deposits  are  frequently  encountered.  It  is  impossible,  how- 
ever, to  ascertain  whether  more  than  one  glacier  extended  over  the  county. 
Resting  on  this  glacial  material  is  a  dark-blue  to  bluish  gray  or  yellow  clay 
known  as  "bowlder  clay,"  a  material  undoubtedly  of  drift  origin.  It  appears 
only  on  the  steepest  slopes  where  the  loess  runs  out:  ordinary  slopes  show  no 
evidence  of  it.  No  great  importance  from  the  agricultural  standpoint  is  there- 
fore attached  to  the  occurrence  of  this  material.     With  the  exception  of  the  steep 

1  Udden  —  Iowa  Geo.  Survey  —  Vol.  XI,  pg.  201. 


POTTAWATTAMIE  COUNTY  SOILS  9 

slopes  mentioned  the  upland  soils  everywhere  are  so  deeply  covered  with  loess 
that  the  underlying  material  has  practically  no  influence  on  the  fertility  of  the 
soil. 

The  loess  is  extremely  variable,  both  in  color  and  composition,  due  of  course 
to  the  varying  conditions  under  which  it  has  existed.  Frequently  lime  material 
occurs  in  considerable  amounts.  It  may  be  rather  uniformly  distributed  thru 
the  loess  but  more  commonly  it  is  collected  into  lumps  or  concretions.  These 
concretions,  or  ''clay  dogs,"  vary  considerably  in  size  and  striking  accumula- 
tions are  occasionally  found  along  the  Missouri  river.  They  are  of  particular 
interest  in  indicating  the  presence  of  sufficient  lime,  or  the  absence  of  acidity, 
in  the  soil. 

The  loess  varies  widely  in  thickness.  It  is  generally  much  thicker  in  the 
western  portion  of  the  county  and  thins  out  somewhat  in  the  east.  The  depth 
may  alter  within  very  short  distances.  The  average  greatest  thickness  in  the 
eastern  portion  of  the  county  is  probably  50  feet  but  it  is  often  less  than  40  feet. 
Along  the  Missouri  river  it  is  usually  70  or  80  feet  in  thickness  and  frequently 
it  becomes  150  to  200  feet  thick. 

The  loess  along  the  rivers  has  of  course  been  modified  to  a  considerable  ex- 
tent by  the  action  of  the  streams  in  carrying  away  and  depositing  material. 
The  terrace  soils,  or  old  bottom  lands,  are  therefore  distinguished  from  the 
loess.  The  present  bottomland  soils  are  likewise  considered  separately.  These 
three  groups  of  soils  constitute  the  basis  for  the  following  discussion  and  de- 
scription of  the  soils  of  Pottawattamie  county. 

PHYSIOGRAPHY  AND  DRAINAGE 

The  topography  of  Pottawattamie  county  is  very  uniform,  consisting  in  the 
main  of  upland  slopes  and  several  flood  plains,  with  some  strips  of  upland  plains 
and  a  few  terraces. 

The  flood  plain  of  the  IVIissouri  river  covers  about  seven  percent  of  the  area. 
The  elevation  of  this  plain  is  generally  less  than  20  feet  above  the  average 
height  of  water  in  the  river.  The  flood  plains  of  the  "West  Nishnabotna  and 
East  Nishnabotna  rivers  are  of  minor  importance,  covering  comparatively  small 
areas.  They  are  on  the  average  from  100  to  120.  feet  above  the  Missouri  river. 
There  are  also  rather  large  plains  or  bottomlands  formed  by  numerous  smaller 
streams. 

The  main  topographic  feature  of  the  county  is  an  old  drift  plain  into  which 
the  lowland  plains  just  described  have  been  cut  and  again  partly  filled.  This 
plain  has  a  gentle  slope  to  the  southwest.  The  average  elevation  above  sea 
level  is  about  1,200  to  1,300  feet. 

The  main  streams  which  cross  the  country  from  north  to  south  divide  this 
plain  into  a  succession  of  broad,  parallel  swells  with  a  central  divide  and  two 
gentle  slopes  doA^-n  to  the  bluffs  of  the  streams.  Thus  the  distinctive,  gently 
undulating  to  hilly  appearance  of  the  loess  soil  area  as  a  whole  is  accounted  for. 

The  rougher  portions  of  the  county,  which  are  found  near  the  bluffs  of  the 
Missouri  river  and  consist  of  numerous  narrow  ridges  and  ravines,  are  undoubt- 
edly the  result  of  erosion.  Thus  the  topography  of  some  areas  has  been  con- 
siderably modified  thru  the  action  of  streams  and  particularly  of  creeks. 


POTTAWATTAMIE  COUNTY  SOILS 


11 


The  drainage  of  Pottawattamie  county  may  be  said  to  have  a  latticed  arrange- 
ment ;  the  heavy,  continuous  lines  of  the  main  streams  run  from  north-northeast 
to  south-west  and  the  small,  more  irregular  lines  of  the  tributaries  run  from 
northwest  to  southeast.  The  lines  of  the  secondary  streams  are  separated  by 
areas  usually  about  four-fifths  of  a  mile  vdde. 

In  general  the  drainage  system  of  the  county  is  excellent.  The  Ea.st  Nishna- 
botna  and  West  Nishnabotna  rivers  and  the  various  creeks  which  run  in  the 
same  direction  as  these  rivers  and  the  tributaries  of  all  these  streams  provide 
thoro  drainage  of  the  county  as  a  Mhole  and  artificial  drainage  is  rarely  neces- 
sary. 

THE  SOILS  OF  POTTAWATTAMIE  COUNTY 

The  soils  of  Pottawattamie  county  may  be  grouped  into  three  general  classes: 
the  loess  soils,  the  terrace  soils,  and  the  swamp  and  bottomland  soils.     There 
are  no  drift  soil  areas  of  sufficient  size  to  be  mapped  and  no  residual  soils. 
TABLE  II.     AREAS  OF  DIFFERENT  GROUPS  OF  SOILS 


Acres 


Per  cent 

72.7 

3.3 

24.0 


Loess 445,760 

Terrace  soils 19  648 

Swamp  and  bottomland  soils 147  072 

Total 612,480  

It  is  apparent  from  table  II  that  the  largest  portion  of  the  countj^,  almost  75 
percent,  is  covered  by  the  loess  soils.  There  is  also  a  rather  large  percent  of 
swamp  and  bottomland  in  the  county.  Terrace  soils  are  found  only  to  a  small 
extent. 

The  terrace  soils  and  the  swamp  and  bottomland  soils  in  Pottawattamie  coun- 
ty are  uniformly  level,  but  the  loess  areas  are  quite  variable.  The  topography 
of  the  Marshall  silt  loam,  the  most  widely  distributed  loess  soil,  ranges  aU  the 
way  from  level  to  hilly,  and  that  of  the  Knox  silt  loam  varies  from  level  to  hilly 
and  in  some  cases  to  rough. 

There  are  ten  distinct  soil  types  in  Pottawattamie  county,  two  loess  soils, 
three  terrace  soils  and  five  swamp  and  bottom-land  soils. 

Table  III  shows  that  the  Marshall  silt  loam  is  not  only  the  chief  loess  soil,  but 

TABLE  III.  TYPES  OF  POTTAWATTAMIE  COUNTY  SOILS  AND  THEIR  AREAS 


Soil  No. 

Types  of  Soils 

Acres 

Percent  of  total 
area  of  county 

LOESS  SOILS 

9 

Marshall  silt  loam 

416,768 
28,992 

68  0 

11 

Knox  silt  loam 

4.7 

TERRACE   SOILS 

23 

Hancock  silt  loam.  .  .  . 

15.744 
3,520 

384 

2  6 

24 
25 

Hancock  silty  clay.  .  .  . 
Osgood  very  fine  sand. 

0.6 
0.1 

SWAMP  AND  BOTTOMLAND  SOILS 

26 
26a 

27 
28 
29 


Wabash  silt  loam 

Wabash  silt  loam   (coUuvial  phase) 

Wabash  silty  clay 

Sarpy  very  fine  sandy  loam 

Sarpy  very  fine  sand 


37,184 
44,864 
51,520 
11,008 
2,496 


13.4 

8.4 
1.8 
0.4 


12  SOIL  SURVEY  OF  IOWA 

it  covers  by  far  the  largest  proportion  of  the  total  area  of  the  county,  over  68 
percent. 

The  other  loess  soil  is  of  much  less  importance,  covering  only  4.7  percent  of 
the  total  area  of  the  county. 

The  terrace  soils  are  all  of  minor  importance,  the  total  area  covered  by  the  three 
being  only  3.3  percent  of  that  in  the  county.  The  Hancock  silt  loam  covers  the 
largest  area  of  the  three  and  the  Osgood  very  fine  sand  is  of  very  small  extent, 
occupying  only  0.1  percent  of  the  area  of  the  county. 

Three  of  the  swamp  and  bottomland  soils  are  rather  extensive  in  area,  the 
Wabash  silt  loam,  the  Wabash  silt  loam  (Colluvial  phase),  and  the  Wabash  silty 
clay.  The  other  two  types  are  of  minor  importance  and  occupy  only  a  small 
part  of  the  county. 

While  the  loess  soils  must  be  considered  first  in  planning  systems  of  soil  man- 
agement for  Pottawattamie  county,  the  swamp  and  bottomlands  should  not  be 
neglected  for  they  are  of  considerable  extent.  Furthermore,  these  latter  soils 
are  much  more  in  need  of  special  treatment  to  make  them  profitably  productive 
than  the  loess  soils,  altho  increases  in  crop  yields  on  the  loess  types  may  also  be 
secured  by  proper  management.  All  the  soil  types  must  be  considered,  there- 
fore, in  working  out  systems  of  permanent  fertility  for  the  county. 

THE  FERTILITY  IN  POTTAWATTAMIE  COUNTY  SOILS 

The  plant  food  content  of  Pottawattamie  county  soils  was  determined  by 
analyzing  samples  of  all  types  found.  These  samples  were  secured  wdth  the 
usual  precautions  that  they  should  be  true  to  type  and  that  all  variations  due 
to  difference  in  treatment  should  be  eliminated.  Three  samples  were  drawn  from 
each  of  the  main  soil  types  and  one  sample  from  each  of  the  minor  types,  just 
as  in  the  case  of  the  other  counties  surveyed.  Each  sample  represented  the 
surface  soil  from  0  to  6%  inches  deep,  the  subsurface  soil  from  6%  to  20  inches 
deep,  and  the  subsoil  from  20  to  40  inches  deep. 

Total  phosphorus,  total  nitrogen,  organic  carbon,  inorganic  carbon  and  lime- 
stone requirement  determinations  were  made  on  the  soils  at  the  three  depths  ac- 
cording to  the  official  methods,  the  Veitch  method  being  employed  for  determin- 
ing the  limestone  requirements 

THE  SURFACE  SOILS 

Table  IV  presents  the  results  of  the  analyses  of  the  surface  soils,  the  figures 
given  being  the  average  of  duplicate  determinations  on  several  samples  of  each 
soil  in  the  case  of  the  major  types.  The  results  are  expressed  in  pounds  per 
acre  of  2,000,000  pounds  of  surface  soil. 

This  table  shows  wide  differences  in  the  plant  food  content  of  the  various  soil 
types.  These  variations  are  noticeable  not  only  when  the  large  soil  groups  are 
compared,  but  also  appear  among  the  types  within  these  groups  To  what  ex- 
tent the  latter  variations  are  due  to  natural  differences  or  to  modifications  brought 
about  by  varying  factors  cannot  be  stated.  It  is  certain,  however,  that  loess 
soils  are  not  necessarily  lower  or  higher  in  any  one  constituent  than  terrace  soils 
or  swamp  and  bottomland  soils,  and  so  on. 

The  phosphorus  content  of  the  terrace  soils  in  Pottawattamie  county  is  gen- 


U.   S.   DEPT.  OF  AGRICULTURE,   BUI 
Milton  Whitney.  Chief.     Curtis.    F.    Marbut, 


SOIL  MAP  OF  POTTAWATTAMIE  COirNTY,  lOWA-Sfiti 


TERRACE  SOILS 


DD 


H  '^ 

SWAMP  AND  BOTTOMLAND  SOILS 


POTTAWATTAMIE  CX)UNTY  SOILS 


13 


erally  higher  than  that  of  the  loess  soils  or  the  swamp  and  bottomland  soils. 
The  organic  carbon  and  the  nitrogen  content  of  the  terrace  soils  are  like\\'ise 
somewhat  greater  than  in  the  loess  soils,  but  the  differences  are  not  large.  The 
swamp  and  bottomland  soils  are  on  the  average  lowest  in  all  three  constituents. 
This  is  unusual  as  such  soils  generally  contain  accumulations  of  organic  matter 
which  lead  to  the  presence  of  greater  amounts  of  organic  carbon,  nitrogen  and 
often  also  of  phosphorus.  It  is  evident  that  in  this  county  these  level,  low-h-ing 
soils  were  originally  lower  in  these  elements  than  the  other  soils. 

The  content  of  inorganic  carbon,  which  in  a  mea.sure  shows  the  lime  require- 
ments of  soil,  is  extremely  variable,  but  it  does  seem  that  the  swamp  and  bottom 
land  soils  are  somewhat  higher  in  this  constituent.  None  of  the  soils  are  acid 
except  the  Marshall  silt  loam,  but  the  supply  of  lime  is  apparently  not  extremely 
high  in  any  of  the  surface  soils. 

None  of  the  soils  in  Pottawattamie  county  are  so  abundantly  supplied  with 
phosphorus  that  this  element  can  be  disregarded  in  systems  of  soil  improvement 
and  permanent  fertility.  There  is  enough  phosphoiiis  in  all  the  soils  for  sev- 
eral crops  if  it  is  made  available  rapidly  enough,  but  when  the  total  phosphorus 
present  is  not  abundant  the  rate  at  which  it  is  made  available  is  certain  to  be 
very  low.  It  is  doubtful,  therefore,  if  sufficient  prosphorus  would  be  made  avail- 
able to  keep  crops  properly  supplied  for  any  considerable  length  of  time.  In 
fact,  in  the  case  of  some  of  the  soil  types  applications  of  phosphorus  might  be 
of  value  at  the  present  time.  This  point  will  be  considered  further  in  connection 
with  the  greenhouse  experiment  on  the  Marshall  silt  loam.  In  general  phos- 
phorus must  be  considered  in  all  systems  of  fertility  which  are  devised  for  the 
soils  of  this  county. 

The  nitrogen  supply  is  low  in  practically  all  Pottawattamie  county  soils. 
Only  in  the  case  of  the  Hancock  silty  clay  is  there  anything  like  a  fair  amount 
of  this  constituent.  The  swamp  and  bottomland  soils  are  notably  low  in  nitro- 
gen, a  rather  unusual  state  of  affairs  as  has  already  been  pointed  out.  The 
organic  carbon  content  of  the  various  soils  is  correspondingly  low  as  is  apt  to 

TABLE    IV.     PLANT    FOOD    IX   POTTAWATTAMIE    COUNTY   SOILS.    IOWA 
POUNDS  PER  ACRE  OF  TWO  MILLION  POUNDS  OF  SURFACE  SOIL  (0-6-%") 


Soil  No. 


Soil  Type 


Total 
phos- 
phorus 


Total 
nitrogen 


Total 
organic 
carbon 


Total 
inorganic- 
carbon 


Lime- 
stone 
require- 
ment 


LOESS  SOILS 


9 
11 


Marshall  silt  loam 
Knox   silt   loam 


1313 
1200 


3260 
1710 


37,S07 
16.065 


146 
4355 


1779 
Basio 


TERRACE  SOILS 


23 
24 
25 


Hancock  sUt  loam 
Hancock  silty  clay 
Osgood  very  fine  sand 


1500 
1900 
1220 


2860 
4380 
1340 


34,104 
52,428 
10.670 


2516 

132 

3070 


Basic 
Basic 
Basic 


SWAMP  AND  BOTTOMLAND  SOILS 


26 

26a 

27 

28 

29 


Wabash  sUt  loam 

Wabash  silt  loam  (Colluvial  phase) 

Wabash  sUty  clay 

Sarpy  very  fine  sandy  loam 

Sarpy  very  fine  sand 


1360 

2820 

1360 

2960 

1380 

1740 

1020 

1780 

840 

440 

38,928 
36,726 
22,644 
15,710 
10,300 


1042 
394 
7236 
4230 
3900 


Basic 
Basic 
Basic 
Basic 
Basic 


14 


SOIL  SURVKY  OF  IOWA 


be  the  case,  the  swamp  ami  bottonihiiul  soils  beiiii;-  particularly  deficient  in  this 
constituent  for  soils  of  such  a  nature. 

All  of  the  soils  are  low  in  orjjanic  nuitter.  That  is  evident  because  the  nitro- 
gen and  organic  carl)on  occur  in  such  relatively  small  amounts  in  practically  all 
cases.  Farm  manure  should  be  applied  in  as  large  amounts  as  practicable  and 
green  manure  crops,  preferably  legumes,  should  be  turned  under  in  order  to 
bring  these  soils  up  to  a  proper  content  of  organic  matter,  and  to  insure  the  best 
mechanical  and  chemical  soil  conditions  for  the  growth  of  bacteria  and  the  pro- 
duction of  available  plant  food. 

The  relation  between  the  carbon  and  nitrogen  in  some  of  these  soils  is  such 
that  there  is  not  the  best  bacterial  action  or  the  best  decomposition  of  the  organic 
matter.  In  some  instances,  therefore,  the  need  of  organic  uuitter  which  will 
undergo  rapid  decomposition  is  very  clearly  shown. 

The  greatest  immediate  need  of  the  soils  in  Pottawattamie  county  is  evidently 
for  organic  matter  and  steps  should  be  taken  to  supply  an  abundance  of  fresh, 
easily  decomposable  material.  Rotations  should  include  a  legume  and  a  green 
manure  "catch  crop."  Crop  residues  should  be  completely  utilized  and  the 
farm  manures  should  be  preserved  carefully  and  applied  in  as  large  quantities 
as  available,  if  permanent  fertility  is  to  be  maintained. 

The  inorganic  carbon  content  of  Pottawattamie  soils  is  comparatively  high. 
In  a  general  way  the  swamp  and  bottomland  soils  are  highest  in  this  constituent. 
The  abundance  of  inorganic  carbon,  reflecting  as  it  does  the  lime  content  of  the 
soil,  indicates  that  the  soils  are  not  likely  to  be  acid  in  reaction.  This  is  the 
case.  Only  one  soil  type  shows  any  limestone  reiiuirement  whatever  and  the 
amount  needed  there  is  small.  Of  the  three  samples  of  the  Marshall  silt  loam 
two  showed   slight   aciditv  and  one   was  basic.     The  average   result   given   in 


Fii 


A   loess  Iduff.     Erosion  is  very  nctivo  on  tlirsc 

ill  tlie  loess 


liills  iiiiil  carves  fantastic  sliapes 


U.  S.   DEPT.  OF  AGRICULTURE,   BURE 
Milton  Whitney,  Chief.     Curtis.   F.   Marbut.  in 


WASHmO 

Douo; 


SOIL  MAP  OK  POTTAAVATTAMIE  ('OIXTY,  lOWA-Seclion  II. 


SWAMP  AND  BOTTOMLAND  SOILS 


# 


POTTAWATTAMIE  COUNTY  SOILS 


15 


table  IV  for  tliis  soil  type  shows,  therefore,  a  small  limestone  re(iuirement.  All 
the  other  soil  types  were  distinctly  basic  in  reaction.  It  is  apparent  that  the 
need  for  applications  of  lime  is  restricted  to  special  cases.  Since  the  chief  soil 
type  in  the  county  is  occasionally  found  to  be  slightly  acid  and  therefore  in  need 
of  lime,  the  soils  in  this  county  should  always  be  tested  for  acidity. 
•  As  a  whole  Pottawattamie  county  .soils  are  particularly  deficient  in  organic 
matter  and  nitrogen  as  well  as  phasphorus  may  be  the  limiting  factor  of  crop  pro- 
duction in  the  near  or  more  or  less  distant  future.  Occasionally  Pottawattamie 
soils  may  be  acid  and  in  need  of  lime.  Applications  of  humus  fonning  mate- 
rials, of  phosphorus  and  of  lime  may  be  necessary  in  many  cases  and  tests  of  the 
value  of  such  materials  should  be  made. 

THE   SUBSURFACE   SOILS  AND   SUBSOILS 
The  results  of  the  analyses  of  subsurface  soil,  and  subsoil  samples  were  cal- 
culated as  pounds  per  acre  of  4,000.000  pounds  of  subsurface  soil  and  of  6,000,- 
000  pounds  of  subsoil.     The  results  are  given  in  tables  V  and  VI. 

TABLE  V.     PLANT  FOOD  IN  POTTAWATTAMIE  COUNTY  SOILS,  IOWA 
POUNDS  PER  ACRE  OF  FOUR  MILLION  POUNDS  OF  SUBSURFACE  SOIL  (6-%-20") 


Soil  No. 


Soil  Type- 


Total 
phos- 
phorus 


Total 
nitrogen 


Total 
organic 
carbon 


Total 
norganic 
carbon 


Lime- 
stone 
require- 
ment 


LOESS  SOILS 

9 
11 

Marshall   silt  loam 
Knox   silt  loam 

1     2600 
1     2340 

5733 
1840 

55,914 

17,838 

298 

14,282 

1223 
Basic 

TERRACE  SOILS 

23 
24 
25 

1   Hancock  silt  loam 
Hancock   silty   clay 
Osgood  very  fine  sand 

1     2800 
3120 
1960 

2840 
6800 
1360 

28,312 

73.016 

6,240 

24,008 

264 

15,000 

Basic 
Basic 
Basic 

SWAMP  AND  BOTTOMLAND  SOILS 

26 

Wabash  silt  loam 

2600 

5520 

52,396 

2964 

Basic 

26a 

Wabash  silt  loam  (Colluvial  phase) 

3040 

6520 

77,112 

968 

Basic 

27 

Wabash   silty   clay 

2760 

3880 

71,416 

17,824 

Basic 

28 

Sarpy  very  fine  sandy   loam 

2000 

2520 

25.560 

8,600 

Basic 

29 

Sarpy   very   fine   sand 

1560 

560 

13,304 

8,136 

Basic 

TABLE  VI.     PLANT  FOOD  IN  POTTAWATTAMIE  (X)UNTY  SOILS.  IOWA 
POUNDS  PER  ACRE  OF  SIX  MILLION   POUNDS  OF  SUBSOIL   (20"-40") 


Soil  No. 


Soil  Type 


Total 
phos- 
phorus 


Total 
nitrogen 


Total 
organic 
carbon 


Total 

inorganic 

carljon 


Lime- 
stone 
rt'(|uire- 
ment 


LOESS  SOILS 


9 
11 


Marshall    silt    loam 
Kno.x  silt  loam 


3700 
3330 


5080 
2070 


65,590 
12,909 


9,230 
22.761 


Basic 
Basic 


TERRACE  SOILS 


23  I   Hancock   silt   loam 

24  I   Hancock   silty  clay 

25  Osgood  very  fine  sand 


26 

26a 

27 

28 

29 


3900 
4260 
3300 


2100 
6600 
1200 


65,844 
63,834 
12,640 


43,596 
426 

22.860 


SWAMP  AND  BOTTOMLAND  SOILS 


Wabash  silt  loam 

Wabash  silt  loam   (Colluvial  phase) 

Wabash    silty    clay 

Sarjiy  very   fine   sandy   loam 

Sarj)y    very    fine    sand 


3960 
5280 
3660 
2700 
2520 


7980 

11280 

4380 

2160 

420 


54,474 
146.628 
40,578 
21.774 
22.050 


1,746 

606 

31,962 

23,706 

11.790 


Basic 
Basic 
Basic 


Basic 
Basic 
Basic 
Basic 
Basic 


Id 


Hon.  HIIU.Vi:V    OK    IOWA 


Nn    llll'Kf    MIIMMIIiIm  (iT   IIIIV    III'    ihr    iKTCSHIiry    |illilll     IntMl    (mmimI  il  lirlild    lire    prcHrlll, 

III  llif  luwcr  Hoil  liiyci'M  willi  llii"  f\cr|il  nm  ol'  imtrjfimic  ('(iilinn.  'Tlic  hiihiiihI  of 
lliH  rlniM'iil.  in  nillior  liii'Kr  in  nmhh'  niNCH  nml  mdirfilcH  llic  iiIinciicc  ol'  iickI  <m)|i- 
JiliotiN.  TIk^  4'uiilriit  ol'  tiili'o).;)-!!  iitiil  oiT-^iiiiir  rtirhon  in  Ilic  HiiliNdrriicc  hoMh 
mill  MiiliNoiJN  In  ^(<ii(M'iiII,v  I(<mn  IIuui  lluil  in  liii<  miii'I'ikm^  soiIh  iih  wuiilii  hi'  rxpi'i'lni, 
itlllio  in  Hfwuii  cMNow  Ihn  (IKI'iM-i'iin'M  hit  vriy  Nli^j^lil.  'riir  piinNpliin'nN  conlcnl  coii- 
hiNlitnlly  ili't'iTfiNi'M  in  llir  lowrr  Moil  Inyi'i'si,  dm  i|  '\h  npl   lo  <lo,  mo  IIiiiI.  llii'tT  '\h  no 

pONNilMlily    of    liny     ilrllrittlKMCN    in     Hum    ilrilirlll     l)ri||,(r    Mllppjlnj     ri'niii     llir    nilili'l' 

lyinf(  soil.  'I'lin  iinioiinl'  Im  loo  hiiiiiII  |o  tlo  iiini-<<  limn  ini-nly  ilrliiy  Mli^lilly  \\w 
tiino  wlirn   plioMpluniiM  nniNl   lio  tipplicil. 

Am  In  llw  (WiMc  ol'  llii'  Minriiri'  Moiin,  only  ono  Noil  lypc  mIiows  iiiiy  in'iilily.  Tlio 
MnliMiirr»M'(>  Noil  ol'  Ilic  MiiihIuiII  Mill  louni  mIiowm  h  niiiiiII  liiiir  rninircincnl,.  Nono 
of  Mie  ollirr  MiiltMnfrin'o  Noilw  sliow  iiny  nctMJ  Tor  liiiir.  In  Ilir  cmho  of  (.lir  hmU 
SoilN.  notU'  of  llio  MiiinplcM  \Vi'n<  lii-nj  II  im  rviilriil,  llirn<rii|-r,  lliiil  in  n-iiir<|y in|^; 
llClillly    III    llir   .'Oil,    lllr    liri'di!   ol'    Ilic   Hlll'I'in'O   Noil    oiil\     inir:l    lir    roiiMy  Irrcil. 

(nU'-.F.N HOUSE  EXPF.RIMKNTS 

Two  M'focnlionNr  r\prriiii<"nlN  wrro  ('iinicil  onl  on  ii  lypicnl  MiirHlmll  Kill,  lomn, 
llu^  iniiin  Noil  lypn  in  I'olliiwiilliitnii^  coiinly.  (>nl^  of  llll^S(<  wns  conilMcli'il  in 
•  !HM)  iinil  llii^  ollirr  wiin  oirnrd  on  m.m  pnrl  ol'  llir  soil  Mnrvey  in    l!>l  I   l;». 

In  llir  IIi'mI  i^sprriiiicnl.  Irii  polM  worr  nsnl,  tlii^  I  n<iil  iiirnlN  conNiMliin^  of  lilll<^ 
in  nil' NlH(^l((Mi  liino,  nilro^^tMi  in  di'iod  hlood,  plioMpliocnH  in  MlrMincd  hone  incnl 
iind  poliiMMiniii  in  Mnli'tdi^  of  poliiMli.  Tito  linir  wmm  npplird  iil  lln'  nilr  ol'  -l/JM) 
poninh  p(^|•  nrrn,  llio  dried  MimxI  nl  llio  vi\\i'  of  '.',(K)0  pounds  ptT  iicir.  Ilif  l)onn 
ni(<id  mI  llio  I'Jilo  (d'  ll»0  ponndsi  pcf  iww  nnd  llir  MiiU'Mlr  ol'  pidiiNli  nl  llir  rule  of 
f)M»  poiind'i  per  iirir 

Wlirat  WUM  jjrowJi  on  llio  poln  mid  llio  >'iiiin  wci^lils  oMninnl  iim  iimiiiI.  'I'lir 
nvsnlls  ol'  llio  oxporiiiii'iil  hit  ^••ivon  in  liiMr   \' 1 1 

'I'lir  limo  luid  no  rlVrcl  on  llir  crop  ^-'own  Wlirii  lilllo>.^rn  WllM  (iddrd  uilli 
llir  llllu^  llirrr  wmm  un  iiirrrjiMo  in  llir  crop       riio',pli(Miis,  iilvrwisr.  Iiroindd   nhonl. 


l''lH.     I,        tiUH'ulum.'U'    i\|riup,i,l      \,.       ■  lliiinillnii'    ulnil 


I'n'r'l'AWA'r'I'AMIK  OnllNTV   Mn||,M 


IT 


'rAIII,!';   VII       OUMKNIUHIHK   I'lM'MIM  M  I'iN'l".    IIHiil 
MAMMIIAI.I,  Mil,'!'  MiAM 

I'll),  Nfi.  'riniiliiinil 

III  (II I( 

IM  I. lino 

li;i  liliiMt    I     NlliiiHon 

(I'i  llllllK      I       I'ImiII||||IIHIN 

Wt  lilino    I     I'lilMMrilnin 

(1(1  lillMII     I      Nlllll^KII      I      |'lllin|llllll  MH 

(17  liliiiii    I    Nllrii(ji<n    |    I'iiImmmImmi 

(IN  lilliin    I     l'lMih|miiMiM    |     I'lilMrtnlnin 

(to  liliiio    I     Nllrii^<i|i    I     l'lMir«|ili)iMin    |     I 'iiliinnliiMi 

7(1  NIlMlf/KII      I      l'llliri|llMIMIM     I      I'llllllillhltll 


WoluM 
(liiiln 

IM  N 
U  tl 

u  ;i 

II  II 

Id  (I 

\o  i 

III   M 

Id  d 

M  ft 


nil   iiK-iriiMr  wlii'ti   iiiiril   willi   llic  I ',   llin  lU'Op  yi«l(l  ll«lll^  jll'tl   iiImhiI    I||«  Mdllic  ItN 

llwil,  m('('III'(m|  wIhii  III"'  mli'HAcii  wnn  nddi'il  I'oIiimmIium  Ii»mI  imi  •'(IVi'I  on  IIm-  i-i'Mp 
NllfOj/cii  lilid  |»li(iM|ilioriin  ii|i|)lli'il  ln>/nlli('r  willi  IIm'  liliM'  ilici'riiMcd  llir  »'r<i|» 
yield  uvci'  lluil    I'.rcini'd    wilh   nirli   nlnnr,   Iml    IIm     iinrc)|Mi«   W(Im  iml    liii|'< 

I'oliiMHiiiiii  Willi  ml  i'np[i'ii  mid  Iiiid'  liiid  iiu  iiilliii'iin' ov*'!-  Ilii'  liiiii',  luid  niliut/rii 
wIhii  iiHrd  Willi  |ilioii|ilinniit  mid  lime  Mlmwrd  no  firii'l  'I'Ih'  yield  in  lldn 
hillrr  i•t\m^  WIIH  even  hoiih'wIiiiI  lower  llimi  willi  llir  eliccK  loil  lo  wliieli  no  I'ec 
lili/er  WWIM  (idded.  Home  linldlOUn  I'lieNM"  evidenlly  nileil'i'icd  Wllll  llie  I'eMllIlM 
lierii.  The  nilroKeii,  (ilioi  |iliio  im  mid  iioIiikmiiiiii  when  nddid  willi  the  linic  ^iive 
lllii  NIIIIK*  yield  tin  when  lie  iiili<i|/ro  mid  |ilioh|ihoniM  were  nited  'IIm  imln  tniui 
nvidenlly  hiid  no  elfcel  in  IIhh  e/iMr  The  nilrof/en,  phoiiphorint  mid  ((ohiniiiiiin 
t((iV(i  iilioiit.  Ihe  Nfinie  ceMiill,  nn  Ihe  nili'opri^n  niid  lime  (ind  Hie  |ihoM|ilioi  im  mid 
\iuu\  hill.  Ihey  liiid  ii,  Hmnller  inlliienen  Ihiin   when   iiMed  wllli   JiiiMv 

II,  in  n|i|iiirenl,  from  llieiiM  reNiillH  llwil,  (loliimiinm  nerd  nol  lie  fi|>|ili<'d  l>i  lln' 
miiiii  WHJ  lype  in  l'oll/iwiill»imie  eonnly.  Lime  liiid  no  ell'i-el  Nilrof/in  mid 
plioM|ihoniN  iincli  hnniKhl.  (iImhiI.  ii  nolieenhle  inereiiNe  in  erop  yield  When  nilio 
(^en  mid  phoMphorni  were  employed  lo(o|||cr,  Ihe  tl)'if\  w/iu  f/renP'r  llimi  lliiil 
produced    hy   e;ieh    (done 

The  Hceond  ex|)erimenl,  eondiielnl  m  IIm'  i/recnliooni'  in  I'M  I  |!*,  involved  Ihe 
more  priielieni  IchIh  of  Ihe  iipplie/dion  oi'  mmiiiie  mid  of  phoNphoriin  in  Ihe  iiviiil 
(ihle  or  (leid  plioM|ihiile  jorm  mid  in  Ihe  roel(  phoHplnile  or  iiiholnhle  form  hime 
wiiH  iipplied  in  Niirijeietd  iimoiinl  lo  niid  riili/,e  Ihe  (teidily  iind  supply  I  wo  Ioiih 
midilion/il ;  mminivt  wuh  iiHed  u\  Ihe  rule  (d'  M)  lonn  per  nere  ;  tieid  phoMphnle  nl, 
f,lie  rule  ol*  'MH)  ponndN  per  nere,  /md  roelt  phoHphnle  nl  Ihe  rule  ol'  l,0(K)  poiimU 
jwr  iicre.  Tim  niHiillx  ol'  Ihin  experiment,  nre,  jriven  in  Inhle  VIII,  Ihe  iiverni/n 
(\vy  weii/hl   in  >/''""•*<  'd'  Ihe  wlieni  ero|»  from  Ihe  diiplieiile  pol«  heinj/  recorded, 

An  exnminnlion  <d'  Inhle  VIII  revenln  Kome  inlerenlinj/  fncjw.  In  Ihe  (Ind 
pinec,  the  /iddilion  of  lime  hroii(;;lil,  (ihnnl,  /i  coriNidenihle  iin'reiiNe  in  Ihe  crop 
yield  TIiIh  HcerriH  to  emplniHi/e  the  fnet,  llnil,  nlllio  lliiM  MnrNlinll  hill  lonm  in  nol, 
f/enernlly  neid,  lin  lime  content,  in  mo  low  Hint,  neid  eondilioiiM  hec/»me  noliec/dde 
in    individiinl   ciiHeH. 

When  roel<  phoiiplint/'  w/ih  /ifiplied  with  the  lime  it,  hnd  no  influence  wlint/'vcr 
(»n  the  er<)p  yield,  Acid  fdioM|dinte  «in  Ihe  other  hnnd  c/ii(H<d  n  deeided  (/din  in 
crop       It   iN  «ivid(!nf,  tlnit,  in  IIm-  nimenee  t,\'  nnlllcient,  orif/inic  ntitWvr,  rorU  pho« 


18 


SOIL  SURVEY  OF  IOWA 


^■■v.r  ■'■■' 


Fig.   5.     Greeiiliouse  expenmeiit   -No.   ~.     The  matiiie  wheat  j^rowiuo-  in  these  pots  shows  tlie 

relative  effect  of  various  treatments  of  Pottaw'attamie  county  soil.     Manure 

used  with  lime  increased  the  yield  four  fold 

phate  has  little  or  no  effect  on  soils  which  are  in  need  of  phosphorus  because 
without  this  organic  matter  the  insoluble  phosphate  is  not  made  available. 

When  manure  was  applied  to  the  soil  with  lime,  a  striking  increase  in  crop 
yield  was  secured,  four  times  as  large  a  crop  being  obtained  as  in  the  untreated 
soil  and  twice  as  large  as  in  the  limed,  unmanured  soil.  The  need  for  organic 
matter  in  the  soil  is  very  distinctly  shown  by  these  r^ults. 

When  rock  phosphate  was  applied  with  the  lime  and  manure  the  crop  yield 
was  apparently  decreased.  Only  one  result  was  secured,  however,  aud  it  should 
not  be  considered  as  it  is  not  probable  that  the  rock  phosphate  would  bring 
about  any  decrease  in  crop.  With  •  '  pho^phat(\  a  iraiii  in  crop  was  secured 
over  that  obtained  in  the  limed,  manured  pot. 

The  results  of  this  experiment  are  shown  in  fig.  5. 

This  greenhouse  experiment  indicated  that  the  piime  need  of  this  soil,  the 
major  soil  type  in  the  county,  is  for  organic  matter.  Applications  of  manure 
would  be  distinctly  valuable  and  if  enough  manure  is  not  available,  green  ma- 
nures should  be  employed.  This  experiment  does  not  include  any  results  to 
show  the  relative  merits  of  farm  manure  and  green  manures  on  this  soil,  but  as 
a  general  thing  farm  manure  is  considered  better  unless  nitrogen  is  decidedly 
deficient  in  which  case  leguminous  green  manure  crops  should  be  grown.  The 
greater  value  of  manure  is  probably  due  to  the  presence  of  numerous  bacteria 
which  bring  about  a  rapid  decomposition  of  the  organic  matter  added  and  hence 
a  rapid  production  of  available  plant  food.  Green  manures  are,  however,  the 
best  substitutes  for  manure  when  the  latter  is  available  only  in  small  amounts. 

Lime  is  shown  to  be  of  use  on  this  particular  soil,  but  no  general  conclusion 


POTTAWATTAMIE  COUNTY  SOILS  19 

TABLE  VI I L     GREENHOUSE  EXPERIMENT,  1915 
MARSHALL  SILT  LOAM 

j  I  Weiglit 
Pot  No.  I  Treatment  I  Grain 
] ' I       g"'s- 

1  I  Check  I       4.37 

2  I  Lime  |       7.75 

3  I  Lime  +  Rofk  Phosphate  I       7.75 

4  I  Lime  +  Acid   Piiosphate  |  10.50 

5  I  Lime  +  Manure  |  17.50 
5      I  Lime -I- Manure  +  Rock   I'liosj.hate  |  11.00* 
7      I  Lime  +  Manure  +  Acid   Phosjihate  1  20. UO 

should  be  drawn  from  these  results  other  than  to  call  attention  to  the  importance 
of  testing  the  soils  of  this  type  to  ascertain  their  reaction  and  need  of  lime. 
When  acid,  lime  should  be  applied.  Furthermore  if  some  areas  of  the  same 
type  are  not  acid,  it  should  not  be  assumed  that  all  areas  are  not  acid.  In 
short,  other  treatments  of  soils  will  be  practically  useless  if  lime  is  not  applied 
when  needed. 

Pliosphorus  in  the  form  of  acid  phosphate  gave  an  appreciable  increase,  botli 
when  applied  with  lime  and  manure  and  with  lime  alone.  The  rock  phosphate; 
used  with  the  lime  alone  gave  no  effects  and  the  results  when  it  was  Employed 
with  the  lime  and  manure  is  (|uestionable,  so  definite  conclusions  cannot  be  drawn 
and  no  comparisons  between  the  two  phosphatic  materials  can  be  made.  It 
would  seem,  however,  that  phosphorus  is  not  present  in  this  soil  type  in  any 
considerable  amounts  and  applications  of  some  phosphatic  material,  if  not  profit- 
able at  the  present  time,  will  undoubtedly  be  necessary  in  the  rather  near  future., 

FIELD  EXPERIMENT 

The  soil  upon  some  of  the  more  hilly  portions  of  the  Missouri  loess  area  in 
Pottawattamie  county  has  sometimes  become  rather  thin  and  occasionally  out- 
crops of  the  underlying  drift  material  occur.  The  removal  of  organic  matter 
from  the  loess  soils,  which  is  generally  rapid,  is  increased  in  such  a  topographic 
sitiiation. 

A  field  ex})eriment  was  conducted  (hiiing  tlie  sea'^ons  of  li)')").  1!)06.  and  1!)07 
to  ascertain  the  needs  of  such  rather  poor  areas  of  Missouri  loe^s  soil.  The  e.x;- 
periment  field  was  located  at  Leeds,  in  Woodbury  county,  near  the  Plymouth 
county  line.  The  general  situation  and  the  conditions  are  very  similar  to  those 
in  Pottawattamie  county  so  that  the  results  of  that  experiment  may  well  be 
considered  here. 

The  complete  data  secured  in  the  experiment  were  presented  in  bulletin  no.  95 
of  the  Iowa  Agricultural  Experiment  Station  published  in  1908  and  hence  only 
summarized  data  and  conclusions  will  be  given  here. 

This  experiment  was  carried  out  on  an  infertile  hilltop,  the  field  being  situated 
on  a  divide  and  the  road  between  the  two  series  of  plots  being  in  the  center  of 
the  i-idge.  The  plots  sloped  east  or  we.st  and  the  general  slope  of  the  area  was 
north  The  soil  was  a  true  loess,  the  underlying  glacial  material  appearinij  only 
in  a  few  places  in  the  vicinity.  The  field  had  been  under  cultivation  for  only 
two  years.     Prior  to  that  time  it  was  in  native  pasture. 

*  The  yield  from  one  pot  discarded. 


20 


SOIL  SUEVEY  OF  IOWA 


On  the  top  of  the  divide  the  organic  matter  content  was  very  low  due  to  the 
constant  removal  of  the  surface  soil  by  erosion  as  well  as  to  rapid  decomposition. 
The  organic  matter  content  of  the  soil  increased  toward  the  lower  part  of  the 
slopes  and  the  gro\\i:h  of  crops  was  much  better  in  these  portions  of  the  plots. 
This  hilltop  was  probably  less  fertile  than  the  most  of  the  area  covered  by  the 
Missouri  loess,  but  it  was  typical  of  a  large  number  of  unproductive  areas  which 
occur  thruout  the  region. 

The  field  was  laid  out  into  44  one-twentieth  acre  plots,  each  1  rod  wide  and  8 
rods  long,  with  a  border  6  feet,  10  inches  wide  separating  it  from  the  next  plot. 

A  regular  four-year  rotation  was  followed,  consisting  of  corn,  corn,  oats,  and 
clover.  The  clover  yields  were  not  secured  separately  so  tliere  are  no  results  for 
this  crop.  The  oats  were  not  threshed  and  hence  the  grain  and  straw  yields  were 
not  secured  separately.  The  total  oats  yield  is  given,  however,  for  the  two  years 
1905  and  1906  and  the  yield  of  com  for  the  years  1905,  1906  and  1907  is  like- 
wise given.     Only  the  weight  of  grain  was  secured  in  the  case  of  the  com. 

The  treatments  of  the  soils  consisted  in  the  application  of  manure  at  the  rate 
of  8  tons  per  acre,  bone  meal  at  the  rate  of  200  lbs.  per  acre  annually,  and  cow- 
peas  for  a  green  manure  by  seeding  the  crop  in  the  com  at  the  last  cultivation 
and  turning  it  under  in  the  spring. 

The  yields  of  oats  are  given  in  table  IX  and  the  average  yields  of  com  for  the 
three  years  appear  in  table  X  together  with  the  average  increase  and  value  of 
the  increase  calculated  on  the  basis  of  bushels  per  acre. 

Little  value  can  be  attached  to  the  oat  results  inasmuch  as  it  is  quite  impos- 
sible to  determine  how  much  of  the  increase  in  total  crop  was  in  the  grain  and 
how  much  was  in  the  straw. 

It  is  apparent  from  the  results  as  a  whole,  that  the  plots  to  which  manure  was 
applied  produced  approximately  one-third  more  grain  and  straw  than  did  the 
plots  which  received  no  manure.  This  is  a  significant  fact,  and  its  importance 
accounts  for  the  inclusion  of  the  data  at  this  place.  It  should  be  kept  in  mind 
in  considering  the  results  secured  by  the  growth  of  com  for  three  years  under 
the  same  treatments. 

The  effects  of  the  various  treatments  on  the  com  crop  are  clearly  shown  in 
table  X  by  the  increases  calculated  for  the  average  yield  for  the  three  years. 
The  cowpeas  gave  a  very  slight  increase,  which  might  be  expected  since  the  crop 
turned  under  was  rather  small.  Manure  gave  a  larger  increase  in  the  yield 
of  corn  and  when  cowpeas  were  applied  mth  the  manure,  a  further  gain  was 
shown. 

TABLE  IX.     FIELD  EXPERIMENT  —  OATS 


Treatment 

1905 

Average  Weight 

Crop 

1906 
Average  Weight 
Crop 

Check 

Manure 

Phosphorus 

Manure  +  Phosphorus 

Potassium   (KQ) 

Manure  -f-  Potassium 

Phosphorus  -|-  Potassium 

Manure  -f  Phosphorus  +  Potassium 

91 
126 

99 
126 

89 
126 
103 
134 

156 
228 
186 
231 

197 
193 
251 

POTTAWATTAMIE  COUNTY  SOILS 


21 


TABLE    X.     FIELD    EXPERIMENT  —  CORN 


1905 

1906       1 

1907 

Aver,  yield]  Aver,  yield |  Aver,  yield 

Average 

Value  of 

bu.  per  acre|bu.  per  acre  bu.  per  acre 

for  3  years 

Increase 

increase* 

Check 

26.7 

36.1 

25.5 

29.4 

Cowpeas 

23.2 

41.1 

27.7 

30.7 

1.3 

$6.43 

Manure 

38.1 

61.5 

39.7 

46.4 

17.0 

5.61 

Manure      ) 
Cowpeas     ] 

44.0 

66.9 

46.1 

52.3 

22.9 

7.56 

Phosphorus    ) 

Cowjjeas          \ 

26.4 

44.9 

31.1 

34.1 

4.7 

1.55 

Phosphorus    1 

Manure           \ 

42.4 

64.9 

47.3 

51.5 

22.1 

7.29 

Phosphorus    j 

Manure           i- 

41.6 

64.0 

49.2 

51.6 

22.2 

7.33 

Cowpeas         J 

Potassium  (K.-SO*)  ) 
Cowpeas                     j 

22.2 

41.9 

28.3 

30.8 

1.4 

0.46 

Potassium     ] 

Manure         } 

34.4 

58.2 

44.7 

45.8 

16.4 

5.41 

Phosphorus    ] 

Potassium       J- 

32.3 

50.5 

34.9 

39.2 

9.8 

3.23 

Cowpeas          1 

Phosphorus    ] 

Potassium       J- 

53.1        1       68.5 

49.3 

57.0 

27.6 

9.11 

Manure           J 

1 

Bone  meal  with  the  cowpeas  had  practically  no  effect  but  with  manure  showed 
a  small  gain  over  the  plot  treated  with  manure  alone.  Potassium  sulfate  ex- 
erted little  influence  on  the  crop  when  used  with  cowpeas  or  with  manure.  A 
slight  gain  was  noted,  both  when  it  was  applied  with  bone  meal  and  cowpeas  and 
when  it  was  used  wdth  bone  meal  and  manure. 

The  beneficial  effect  of  the  manure  is  the  most  prominent  fact  brought  out  by 
the  results  as  a  whole.  It  shows  its  influence  distinctly  in  each  crop,  as  well  as 
in  the  general  average.  The  calculation  of  the  value  of  the  increases  due  to  the 
various  treatments  shows  a  large  value  for  the  manure. 

Evidently,  altho  prosphorus  was  not  abundant  in  these  infertile  hill  tops,  the 
use  of  sufficient  organic  matter  encouraged  decomposition  processes  and  the  pro- 
duction of  available  phosphorus  to  such  an  extent  that  the  addition  of  a  phos- 
phate fertilizer  did  not  give  large  increases.  The  same  is  true  of  potassium  sul- 
fate. The  large  increase  in  crop  brought  about  by  the  manure  may  have  been 
due  in  part  to  the  plant  food  supplied  in  the  material,  but  by  far  the  greatest 
effect  was  probably  due  to  the  organic  matter  introduced  which  brought  about 
an  improvement  of  the  physical  condition  of  the  soil.  The  ability  to  retain 
moisture,  less  extensive  aeration  and  consequently  better  bacterial  action,  with 
the  more  economic  production  and  utilization  of  plant  food,  are  the  direct  results 
of  the  application  of  manure  to  this  soil. 

The  system  of  management  recommended  for  the  improvement  of  the  hilltops 
in  the  Missouri  loess  area  involves,  therefore,  the  maintenance  of  a  sufficient 
supply  of  organic  matter.  This  may  be  accomplished  by  the  use  of  manure  and 
by  the  proper  rotation  of  crops.  The  rotation  used  should  include  the  growing 
at  frequent  intervals  of  a  crop  which  leaves  a  large  portion  of  its  material  on 
the  land  and  clover  is  the  best  crop  for  this  purpose. 


*  Value  calculated  on  basis  of  33  cents  per  bushel. 


22  SOIL  SURVEY  OF  IOWA 

When  this  crop  is  grown  and  the  seed  only  is  removed,  or  even  where  the  first 
crop  is  cut  and  fed,  there  is  considerable  value  in  clover  from  the  standpoint  of 
maintaining-  the  organic  matter  content  of  the  soil.  It  is  a  valuable  addition  to 
fanu  manure  which  so  oft^n  is  not  produced  in  large  enough  amounts  to  keep 
up  all  the  soil  on  a  farm. 

FIELD  EXPERIMENTS  WITH  GUMBO 

Within  the  state  there  are  areas  of  soil  popularly  called  "gumbo"  which  have 
received  special  attention  for  several  years  because  of  the  difficulty  in  farming 
them  and  because  of  their  need  for  special  treatment. 

The  term  "gumbo"  is  not  a  recognized  name  for  a  particular  class  of  soils, 
according  to  any  accepted  scheme  of  soil  classification.  It  is  a  popular  name 
for  a  group  of  soils  which  pos«eSvS  characteristics  well  known  and  dreaded  by 
farmers.  It  is  very  different  from  the  gumbo  referred  to  in  geological  reports 
which  includes  almost  impervious  gray  or  yellow  clay  subsurface  soils. 

The  soil  that  Iowa  farmers  call  "gimibo"  is  a  heavy,  "greasy"  black  clay 
soil,  occurring  in  flat  areas,  either  river  bottoms  or  level  uplands.  It  is  usually 
inky  black  and  is  stickier  and  bakes  more  easily  than  any  other  type  of  soil  in 
the  state.  If  such  soil  is  plowed  when  too  wet  it  balls  up  before  the  plow  point 
in  such  a  way  that  the  best  implement  cannot  be  made  to  stay  in  the  ground. 
On  the  other  hand,  if  it  becomes  too  dry  it  will  turn  up  in  clods  which  cannot  be 
worked  down  during  the  whole  season.  Where  such  clods  are  formed,  freezing 
and  thawing  is  the  only  process  which  will  restore  the  loose,  mealy  structure. 
This  soil  can,  however,  be  put  in  excellent  tilth,  with  a  fine,  mealy  appearance 
and  kept  so  during  the  entire  season  provided  it  is  not  cultivated  when  too  wet. 

The  total  area  of  "gumbo"  in  Iowa  is  probably  about  1  percent  of  the  entire 
state,  occurring  in  small  patches  in  various  localities.  The  principal  areas  are 
in  southeastern  Iowa  and  along  the  Missouri  river  in  western  Iowa.  The  coun- 
ties'in  which  "gumbo"  has  been  found  are  Muscatine,  Washington,  Louisa. 
Henry,  Des  Moines,  Van  Buren,  Lee,  Woodbury,  Monona,  Harrison  and  Potta- 
wattamie. 

Pottawattamie  county  has  a  typical  "gumbo"  soil,  known  as  the  Wabash  silty 
clay.  It  covers  about  8  percent  of  the  area  of  the  county  and  occupies  level  or 
depressed  areas  wdthin  the  broader  bottomlands.  The  management  of  "gumbo" 
may  profitably  be  considered  at  this  point,  therefore,  and  the  results  of  a  field 
experiment  presented.  While  this  experiment  was  not  carried  on  in  this  county, 
it  yielded  results  applicable  to  "gumbo"  soils  everywhere  in  the  state. 

This  experiment  was  located  on  a  typical  area  of  "gumbo"  bottomland  near 
Wapello,  Louisa  county.  Two  series  of  plots  were  laid  out  in  1908,  one  consist- 
ing of  six  plots  which  were  undrained  and  one  of  ten  which  were  as  well  drained 
as  conditions  would  permit.  The  treatment  and  yields  of  corn  in  1909  are  given 
in  table  XI. 

Plots  101,  102,  103,  201  and  202  were  green  manured  in  1908  with  rape,  buck- 
w'heat,  clover  and  clover  and  timothy,  respectively.  The  clover  and  timothy 
on  plots  201  and  202  had  been  a  meadow  for  several  years  and  produced  a  crop 
of  hay  in  1908  which  made  a  yield  of  21/0  tons  per  acre.     The  aftermath  was 


POTTAWATTAMIE  COUNTY  SOILS 
TABLE    XL      FIELD   EXPERIMENTS   ON   "GUMBO' 


23 


Plot  No. 


Treatment 


Lu.  corn  per  acre 
1909 


1             Drained 

101 

1     Rape    (too   wet) 

102 

1     Buckwheat 

103 
104 

1     Clover 
1     Check 

105 

1     Lime — -10  T  jier  acre 

106 

Straw  —  4   T   per   acre 

107 

1     Clieck 

108 

1     Manure — 12   T   per  acre 

(too 

wet) 

109 

1     Manure —    6   T   j  er  acre 
I'lidraincd 

(too 

wet) 

201 

Clover  and  tiniotliv  sod 

202 

1     Clover  and  timothy  sod 

20:J 

1     Manure — -12  T  per  acre 

204 

1     Check 

205 

Manure  —  sprino-  plowed 

L(I6 

(.'!:eck  —  sprinjr    i  Inweil 

24 
62 
94 
77 
68 
47 
40 
2:5 
14 

7 
10 
15 
27 
20 
20 


plowed  under  for  green  nuinuie.  All,  except  plots  205  and  206,  were  fall  plowed 
in  1908,  the  treatments  indicated  being  made  prior  to  plowing. 

In  Uie  fall  plowing  it  was  noticed  that  the  clover  and  buckwheat  plots  worked 
much  more  easily  than  tiie  others.  The  following  season  the  plots  which  re- 
ceived manure  dried  out  more  slowly  after  a  wet  spell  than  the  others.  Fur- 
ther observations  on  the  effects  of  treatment  could  not  be  made. 

Great  differences  in  yield  occurred  but  these  should  undoubtedly  be  attributed 
to  differences  in  drainage  rather  than  to  the  effects  of  treatment.  It  was  im- 
possible to  get  a  satisfactory  outlet  for  the  tile  drain  and  on  each  side  of  the 
experiment  field  there  was  a  swampy  place  in  which  the  water  stood  nearly  all 
summer  and  this  surely  affected  the  results  from  the  outside  plots.  (101,  108, 
109). 

Where  the  soil  was  fall  plowed,  a  fine  mealy  seed  bed  was  obtained  for  the 
corn  which  was  planted  on  May  13.  Surrounding  undrained  land  which  was 
not  fall  plowed  could  not  be  planted  until  about  June  10.  The  undrained  plots 
were  too  wet  nearly  all  summer  and  the  outside  plots  in  the  drained  series  were 
also  too  wet.  In  the  latter  part  of  the  summer  all  of  the  plots  dried  out  well 
at  the  surface  and  the  undrained  ones  cracked  open,  leaving  wide  fissures  to  a 
depth  of  more  than  a  foot.  On  the  best  drained  plots,  th(>  fine  crumbly  surface 
soil  prevented  this  cracking.  On  the  hard,  cracked  ground  the  corn  turned 
yellow  and  "fired"  about  the  middle  of  August,  but  on  the  other  plots  it  re- 
mained green  at  least  three  weeks  longer. 

The  fall  plowed  plots  were  fairly  clean  of  weeds  and  grass  while  the  others 
were  very  foul.  The  lime  treatment  of  plot  105  seemed  to  have  no  effect  on 
the  "gumbo." 

This  experiment  shows  very  definitely  •  the  possibilities  of  "gumbo"  soils 
.when  properly  drained  and  fall  plowed.  The  drainage  of  "gumbo"  is  more 
readily  accomplished  than  would  be  supposed.  On  the  upland  the  tile  should 
be  laid  8  rods  apart  to  secure  good  drainage,  altho  reports  have  been  made  of 
successfully  drained  "gumbo"  when  the  tile  was  10  to  12  rods  apart.  On  the 
lowland  "gumbo"  the  tile  should  be  somewhat  closer  together,  but  the  securing 


24  SOIL  SUEVEY  OF  IOWA 

of  a  satisfactory  outlet  is  the  chief  necessity  for  thoro  drainage  and  in  some 
eases  it  may  be  necessary  to  run  an  open  ditch  thru  to  the  river,  in  wihich  case  a 
drainage  district  must  be  organized.  Wlien  properly  tiled  out  such  ''gumbo" 
soil  is  equal  to  any  other  soil  in  the  state  in  producing  power  for  general  farm 
crops.  Fall  plowing  improves  the  soil  very  decidedly  and  the  use  of  clover  or 
some  other  green  manure  is  also  of  value.  Lime  apparently  is  of  no  use  on  such 
soils. 

The  occurrence  of  "gumbo"  on  a  farm  need  not  be  a  cause  of  lower  value 
of  the  farm.  It  may  be  made  and  kept  productive  thru  the  treatments  men- 
tioned above  and  is  then  equal  in  value  to  the  best  farm  land. 

THE  NEEDS  OF  POTTAWATTAMIE  COUNTY  SOILS  INDI- 

GATED  BY  CHEMICAL,  GREENHOUSE 

AND  FIELD  TESTS 

MANURING 

The  value  of  a  sufficient  amount  of  organic  matter  in  soils  is  well  known. 
Commercial  plant  food  materials  alone  are  quite  insufficient  to  keep  a  soil  in 
the  proper  condition  for  satisfactory  growth.  The  physical  conditions  soon 
become  unfavorable,  bacterial  action  is  restricted  and  the  plant  food  present  in 
the  soil  largely  remains  in  its  normally  useless  condition  if  the  organic  matter 
or  humus  content  of  the  soil  becomes  low. 

The  soils  of  Pottawattamie  county  are  noticeably  deficient  in  organic  matter 
even  in  the  case  of  swamp  and  bottomland  soils,  which  is  unusual.  Potta- 
wattamie soils  are  so  open  and  thoroly  aerated  that  the  decomposition  of  organic 
matter  proceeds  at  a  veiy  rapid  rate.  The  accumulation  of  organic  matter 
from  plant  residues  is,  therefore,  very  slow,  if  any  increase  at  all  occurs.  In 
fact,  in  a  great  majority  of  cases  there  has  been  a  gradual  loss  of  humus,  the 
removal  of  organic  matter  by  decomposition  having  proceeded  faster  than  the 
addition  of  material  thru  the  ordinary  methods  of  cropping  which  are  followed. 
Furthermore,  with  this  rapid  removal  of  organic  matter  there  has  been  a  con- 
tinual loss  of  plant  food  thru  the  production  of  greater  amounts  of  available 
food  than  necessary  for  the  crops  grown.  If  the  loess  soils  had  not  been  espe- 
cially well  supplied  with  plant  food  origiually,  still  greater  deficiencies  in  cer- 
tain constituents  would  be  found  now.  These  soils  were  once  evidently  very 
rich  in  plant  food,  especially  in  lime,  and  hence  in  spite  of  the  large  losses,  their 
supply  of  food  constituents  is  not  generally  depleted  to  a  danger  point.  How- 
ever, if  steps  are  not  taken  in  the  near  future  to  check  the  heavy  losses  that  are 
going  on  the  time  will  soon  come  when  extreme  measures  will  be  necessary  to 
make  the  soils  profitably  productive.  Better  methods  of  management  than  are 
at  present  followed  will  not  only  prevent  the  wearing  out  of  the  soils,  but  will 
also  make  them  more  productive  immediately. 

The  laboratory,  greenhouse  and  field  tests  show  beyond  doubt  that  organic 
matter  should  be  used  on  these  soils  to  increase  their  fertility  and  keep  them 
fertile.  Organic  matter  may  be  added  in  the  form  of  farm  manure,  green 
manures  and  crop  residues  and  all  three  should  be  used. 


POTTAWATTAMIE  COUNTY  SOILS  25 

Crop  residues,  consisting  of  the  straw,  stover,  roots  and  stubble  of  crops,  add 
considerable  organic  matter  or  humus  and  also  return  much  plant  food  to  the 
soil.  Under  ordinary  farming  conditions  roots  and  stubble  remain  in  the  soil. 
Too  often,  however,  the  straw,  and  stover  are  not  returned.  Nothing  should 
interfere  with  the  return  of  these  materials.  On  the  livestock  farm  they  should 
be  utilized  for  feed  and  bedding  and  returned  in  the  manure  and  on  the  grain 
farm  they  should  be  even  more  carefully  used,  because  the  manure  which  has 
additional  value  is  not  available.  The  "life"  of  a  soil,  or  the  time  during  which 
it  will  remain  productive,  is  much  longer  where  the  crop  residues  are  carefully 
utilized. 

Crop  residues  alone  are  insufficient,  however,  to  keep  up  the  organic  matter 
supply  in  soils.  This  fact  is  especially  noticeable  in  the  loess  soils,  such  as  are 
found  in  Pottawattamie  County,  Farm  manures  and  green  manures  must  be 
used  in  addition. 

Farm  manure  supplies  a  large  amount  of  organic  matter  and  considerable 
plant  food  and  besides  it  adds  enormous  numbers  of  bacteria.  These  organisms 
are  responsible  for  decomposition  processes  and  hence  bring  about  the  produc- 
tion of  available  plant  food  in  the  soil. 

The  value  of  farm  manure  on  the  Marshall  silt  loam,  the  main  soil  type  in 
Pottawattamie  county,  has  been  well  shown  by  the  greenhouse  and  field  results 
referred  to  earlier  in  this  report.  No  other  material  apparently  can  take  its 
place  in  increasing  crop  production.  The  experiment  with  the  rather  infertile 
hill  top  soil  showed  especially  the  great  value  of  manure  in  making  this  soil 
more  productive..  Other  fertilizing  materials,  while  of  some  value,  had  com- 
paratively small  effects.  All  the  manure  produced  on  the  livestock  farm,  should, 
therefore,  be  added  to  the  soils.  Furthermore,  the  manure  should  be  very  care- 
fully stored  while  awaiting  use.  Great  losses  may  occur  thru  improper  storage 
and  the  more  readily  available  and  valuable  plant  food  may  disappear  almost 
entirely.  As  much  as  85%  of  the  valuable  matter  in  manure  may  be  lost  thru 
careless  handling.  The  ordinary  application  of  10  tons  of  manure  to  the  soil 
once  in  the  four-year  rotation  is  not  sufficient  to  keep  soils  fertile  indefinitely. 
The  soils  of  Pottawattamie  county,  and  particularly  the  Marshall  silt  loam, 
should  receive  heavier  applications  at  the  present  time  to  improve  their  physical 
condition  and  make  them  more  productive.  Too  large  amounts  are  not  likely 
to  be  applied  because  of  the  lack  of  material,  but  16  to  20  tons  per  acre  should 
not  be  exceeded. 

On  livestock  farms  manure  may  often  be  applied  as  recommended,  but  on 
grain  farms  green  manure  crops  must  be  used  in  place  of  manure.  Further- 
more, farm  manure  is  not  alone  sufficient  to  keep  the  soil  fertile  and  green  ma- 
nures also  have  a  place  on  livestock  farms.  Green  manure  crops  are  so  varied 
that  they  may  be  employed  under  almost  any  conditions.  Legumes  are  par- 
ticularly valuable  because  when  well  inoculated,  as  they  should  be,  they  take 
nitrogen  from  the  air  and  thru  their  use  the  nitrogen  content  of  the  soil  may  be 
increased.  At  the  same  time  such  crops  supply  organic  matter  as  well  as  do  non- 
legumes. 

There  can  be  no  question  of  the  value  of  such  green  manures  on  the  soils  of 


26  SOIL  SURVEY  OF  IOWA 

Pottawattamie  county.  The  experiment  reported  hardly  gives  a  fair  evidence 
of  their  value,  inasmuch  as  the  cowpeJi  crop  was  so  small.  Tlu'v  should  be 
used  in  addition  to  farm  manures,  either  by  introduction  into  the  rotatiim  as 
"catch"  crops  or  by  turning  under  a  full  season's  crop.  The  relative  merits 
of  farm  manures  and  green  manures  need  not  be  considered  here,  for  both  are 
valuable  and  the  latter  should  be  regarded  as  supplementing  or  taking  the  place 
of  the  former.  It  is  often  advisable  to  make  a  small  application  of  farm  ma- 
un ic  jilong  with  a  green  manure  crop  to  start  the  necessary  decomposition. 

There  are  some  dangers  in  the  use  of  green  manures,  chiefly  in  the  reduction 
of  soil  moisture,  which  may  occur  in  turning  under  a  large  crop.  In  dry  sea- 
sons the  time  for  turning  under  a  green  manure  crop  should  be  carefully  chosen 
to  avoid  any  injurious  action.  The  crop  should  be  green  and  full  of  moisture, 
for  it  decomposes  more  rapidly  under  those  conditions,  and  it  should  be  plowed 
under  before  the  soil  is  cool.  Both  green  manures  and  farm  manures  should 
1 1'  us((l  with  care  and  common  sense  and  then  there  will  be  no  danger  in  their 
employment. 

In  choosing  the  crop  for  a  green  manure,  select  one  which  will  be  suitable  for 
the  particular  soil  and  climatic  conditions  and  which  will  not  interfere  with 
the  regular  rotation.  The  cost  of  seeding  and  the  monetary  value  of  the  crop 
for  hay  or  pasture  should  also  be  considered. 

Acid  conditions  in  the  soil  are  increased  by  the  use  of  all  materials  furnish- 
ing organic  matter  and  the  lime  content  of  the  soil  must  be  carefully  looked 
after  if  farm  manure  or  green  manures  are  employed. 

COMMERCIAL  FERTILIZERS 

Pottawattamie  county  soils  do  not  have  an  abundance  of  nitrogen  or  phos- 
phorus and  hence  it  might  be  assumed  that  applications  of  commercial  fer- 
tilizers might  prove  profitable.  The  greenhouse  and  field  experiments  show, 
however,  that  such  materials  do  not  give  large  increases  in  crop  yields. 

Nitrogen  should  not  be  applied  as  a  commercial  fertilizer  as  long  as  it  is 
possible  to  keep  up  the  supply  by  the  use  of  leguminous  green  manure  crops. 
Connnercial  nitrogenous  materials  should  be  used  on  Iowa-  soils  only  in  special 
ca.ses  where  a  certain  crop  needs  an  initial  stimulus  or  where  experiments  have 
shown  them  to  be  profitable.  Leguminous  green  manures  are  cheaper  and  have 
the  additional  value  of  maintaining  the  organic  matter  supply  in  the  soil. 

Phosphorus  is  not  abundant  in  Pottawattamie  county  soils,  but  while  appli- 
cations of  phosphates  bring  about  some  gains,  they  do  not  always  give  suffi- 
cient crop  increases  to  warrant  their  use.  Compared  with  the  use  of  manure, 
the  use  of  phosphorus  is  of  small  value.  When  added  with  manure  it  brings 
about  only  small  gains.  Altho  the  amount  of  phosphorus  is  low  in  loess  soils, 
when  organic  matter  or  humus  is  snpi)lied  and  the  soil  bacteria  are  active,  enough 
phosphorus  becomes  available  in  the  soil  to  supply  crop  needs  and  at  present 
additions  of  phosphorus  do  not  increase  yields  to  any  large  extent.  The  amount 
of  phosphorus  in  some  of  the  other  soils  of  the  county  is  less  than  that  in  the 
Marshall  silt  loam  and  on  such  soils  the  effects  of  phosphorus  fertilizers  might 
be  greater. 

While  farm  yard  manure  returns  some  of  the  phosphorus  removed  from  soils 


POTTAWATTAMIE  COUNTY  SOILS  27 

by  crops,  the  amount  available  on  the  average  farm  is  entirely  too  small  to  keep 
up  the  supply  of  phosphorus.  Sooner  or  later  commercial  phosphorus  fer- 
tilizers will  be  necessary.  Unfortunately  the  experiments  thus  far  carried  out 
on  the  loess  soils  do  not  show  definitely  which  form  of  phosphorus  fertilizer 
should  be  emi)loyed.  Bone  meal  was  used  in  tht^  field  lest  and  the  results 
showed  an  increase,  but  bone  meal  cannot  be  recommended  because  of  the  diffi- 
culty in  obtaining  it.  That  leaves  a  choice  between  the  insoluble  rock  phos- 
phate and  the  soluble  acid  phosphate.  The  greenhouse  experiment  showed  slight 
gains  from  acid  phosphate  while  the  rock  phosphate  for  some  unknown  reason 
depressed  the  yield.  This  must  be  regarded  as  an  accidental  result  and  hence 
no  comparison  of  the  two  materials  is  possible  at  the  present  time  and  no  rec- 
ommendation of  one  over  the  other  can  he  made.  Field  experiments  carried 
out  under  a  wide  variety  of  soil  conditions  are  necessary  in  order  to  reach  defi- 
nite conclusions.  Fanners  are  urged  to  test  both  materials  under  ordinary 
farming  conditions.  Complete  directions  for  such  tests  and  advice  for  specific 
conditions  will  be  given  by  the  Soils  Section  upon  application  by  farmers. 

No  analyses  for  potassium  were  made  of  Pottawattamie  county  soils  for  this 
element  is  so  abundant  in  all  the  soils  of  the  state  that  it  hardly  seemed  necessary. 
In  the  field  experiment  with  the  hill  top  soil  a  few  tests  were  made  with  potas- 
sium, and  while  a  slight  gain  was  secured  in  one  ease,  in  general  the  effect  was 
practically  negligible.  It  is  evidently  true  that  potassium  fertilizers  are  un- 
necessary on  the  soils  of  Pottawattamie  county  at  the  present  time.  Only  where 
special  crops  need  stimulation  during  the  early  stages  of  their  growth  should 
potassium  salts  be  applied. 

It  is  apparent  that  the  maintenance  of  the  permanent  fertility  of  Potta- 
wattamie soils  does  not  require  the  application  of  complete  commercial  fertiliz- 
ers. Potassium  is  not  necessary  and  will  not  be  needed  for  a  long  time.  Nitro- 
gen is  low,  but  this  can  be  more  cheaply  and  better  supplied  in  leguminous  green 
manure  crops  than  in  commercial  nitrogenous  fertilizers.  Phosphorus  is  the . 
only  element  which  must  be  supplied  in  a  commercial  form.  The  amount  pres- 
ent is  so  small  that  evidently  means  must  soon  be  taken  to  replenish  the  supply. 
Just  what  form  of  phosphorus  fertilizer  to  employ  cannot  be  definitely  stated 
now  and  neither  can  the  value  of  its  use  at  the  present  time  be  given. 

LIME 

The  soils  in  Pottawattamie  county  are  generally  well  supplied  with  lime,  but 
some  types  are  low  in  lime  and  therefore  need  applications  of  this  material 
from  time  to  time  to  keep  them  from  becoming  acid.  For  example,  the  Marshall 
silt  loam  is  occasionally  acid.  All  of  the  soils  in  this  county  should  be  carefully 
tested  for  acidity,  and  especially  the  upland  loess  and  hill  top  soils.  The  appli- 
cation of  other  necessary  fertilizei's  will  be  practically  useless  if  lime  is  lacking 
in  the  soils.  The  use  of  organic  matter,  which  has  been  shown  to  bring  about 
such  striking  increases  in  yields,  would  not  prove  as  valuable  in  the  absence 
of  lime.  Furthermore,  those  soil  types  which  are  apparently  well  supplied  with 
lime  at  the  present  time  will  gradually  lose  it.  The  use  of  organic  matter  will 
increase  the  production  of  acids  which  will  in  turn  cause  the  rapid  disappear- 
ance of  lime.     Whenever  the  crop  producing  power  of  a  soil  rich   in   lime  is 


28  SOIL  SURVEY  OF  IOWA 

increased  by  proper  methods  of  treatment,  lime  is  rapidly  removed  and  must 
be  supplied  eventually. 

If  tests  show  a  soil  to  be  acid,  three  to  four  tons  of  lime  will  supply  all  that 
is  necessary  for  several  years  on  practically  any  soil  in  Pottawattamie  county. 
This  amount  will  neutralize  all  the  acidity  and  leave  two  tons  additional  in  the 
soil.  Such  an  amount  applied  in  a  four-year  rotation  will  keep  the  soil  in  the 
proper  condition  for  crop  gro'«i;h  as  far  as  acidity  is  concerned.  However,  the 
very  best  results  are  always  secured  by  testing  each  soil  and  applying  the  amount 
which  the  soil  is  found  to  need. 

DRAINAGE 

Practically  all  the  soils  in  Pottawattamie  county  are  well  drained.  In  fact, 
most  of  them  are  too  thoroly  drained.  They  are  so  open,  and  so  well  aerated 
that  the  organic  matter  content  has  been  rapidly  decreased  and  valuable  plant 
food  has  been  lost.  In  general,  therefore,  there  is  more  need  in  this  county  for 
the  adoption  of  methods  of  retaining  moisture  in  the  soils  than  of  providing 
drainage. 

There  are  two  soil  types,  however,  the  Hancock  silt  loam,  a  terrace  soil,  and 
the  "Wabash  silty  clay,  a  bottomland  soil,  which  show  the  need  of  drainage  in 
their  level  portions.  The  poorly  drained  areas  of  these  types  are  small  and 
hence  drainage  cannot  be  considered  of  great  importance  in  the  county.  But 
whenever  it  is  necessary,  an  efficient  drainage  system  should  be  installed.  No 
amount  of  fertilization,  care  or  treatment  of  any  kind  will  offset  the  injurious 
effect  of  poor  drainage. 

ROTATION  OF  CROPS 

For  the  continued  fertility  of  any  soil,  a  well  defined  crop  rotation  should  be 
followed.  The  continuous  growing  of  any  one  crop  seems  to  deplete  the  soil 
very  rapidly  and  to  reduce  crop  production. 

Whatever  rotation  of  crops  is  used,  legumes  should  be  included  and  green 
manure  crops,  crop  residues  and  farm  manure  should  be  carefully  employed 
to  build  up  and  keep  up  the  organic  matter  in  the  soil.  Definite  rotations  are 
difficult  to  suggest,  owing  to  the  ^vide  range  of  conditions  which  must  be  met, 
but  the  following  would  serve  quite  satisfactorily  in  many  eases: 

1.     FOUR  OR  FIVE-YEAR  ROTATION 

First  year:  Corn  (with  cowpeas,  rape,  or  rye  seeded  in  the  standing  corn  at  the  last  cultiva- 
tion). 

Second  year:     Corn. 

Third  year:     Oats  (with  clover  or  with  clover  and  timothy). 

Fourth  year:  Clover.  (If  timothy  was  seeded  with  the  clover,  the  preceding  year,  the  rota- 
tion may  be  extended  to  five  years.     The  last  crop  will  consist  principally  of  timothy). 

2.     FOUR- YEAR  ROTATION  WITH  ALFALFA 
First  year:     Corn. 
Second  year:     Oats. 
Third  year:     Clover. 
Fourth  year:     Wheat. 

Fifth  year:     Alfalfa.     (This  crop  may  remain  on  the  land  five  years.     This  field  should  then 
be  used  for  the  four-year  rotation  outlined  above). 

3.     THREE-YEAR  ROTATION 

First  year:     Corn. 

Second  year:     Oats  or  wheat  (with  clover  seeded  in  the  grain). 

Third  year:     Clover.     (Only  the  grain  and  clover  seed  should  be  sold;  in  grain  farming  most 

of  the  crop  residues,  such  as  corn  stover  and  straw  should  be  plowed  under.     The  clover 

may  be  clipped  and  left  on  the  land  to  be  returned  to  the  soil). 


POTTAWATTAMIE  COUNTY  SOILS  29 

In  livestock  fanning  the  products  grown  in  the  rotation  should,  for  the  most 
part 'be  fed  or  used  for  bedding  and  the  manure  carefully  saved  and  used  as 
a  fertilizer. 

"Catch"  crops,  such  as  cowpeas,  soybeans,  vetch  and  clover  seeded  in  stand- 
ing com,  are  frequently  unprofitable  in  Iowa  because  of  the  high  cost  of  the 
seed  and  the  failure  of  the  crop  to  make  a  satisfactory  growth.  The  non- 
legumes,  such  as  rye  and  rape,  usually  do  well  when  seeded  in  standing  com. 

THE  PREVENTION  OF  EROSION 

Erosion  is  the  carrying  away  of  soil  thru  the  free  movement  of  water  over 
the  surface  of  the  land.  If  all  the  rain  falling  on  the  ground  were  absorbed, 
erosion  could  not  occur,  hence  it  is  evident  that  the  amount  and  distribution  of 
rainfall,  the  character  of  the  soil,  the  topography  or  the  "lay  of  the  land," 
and  the  cropping  of  the  soil  are  the  factors  which  determine  the  occurrence  of 
this  injurious  action. 

Slowly  falling  rain  may  be  very  largely  absorbed  by  the  soil,  provided  it  is 
not  already  saturated  with  water,  while  the  same  amount  of  rain  in  one  storm 
will  wash  the  soil  badly.  When  the  soil  is  thoroly  wet,  the  rain  falling  on  it 
will  of  course  wash  over  it  and  much  soil  may  be  carried  away  in  this  manner. 

Light,  open  soils  which  absorb  water  readily  are  not  apt  to  be  subject  to  ero- 
sion while  heavy  soils  such  as  loams,  silt  loams  and  clays  may  suffer  much  from 
heavy  or  long-continued  rains.  Loess  soils  are  very  apt  to  be  injured  by  erosion 
when  the  topography  is  hilly  or  rough  and  it  is  this  group  of  soils  which  is 
affected  to  the  greatest  extent  in  Iowa.  Flat  land  is,  of  course,  little  influenced 
by  erosion.  Cultivated  fields  or  bare  bluffs  and  hillsides  are  especially  suited 
for  erosion  while  land  in  sod  is  not  affected.  The  character  of  the  cropping  of 
the  soil  may  therefore  determine  the  occurrence  of  the  injurious  action.  The 
careless  management  of  land  is  quite  generally  the  cause  of  the  erosion  in  Iowa. 
In  the  first  place,  the  direction  of  plowing  should  be  such  that  the  dead  furrows 
run  at  right  angles  to  the  slope;  or  if  that  is  impracticable,  the  dead  furrows 
should  be  "plowed  in"  or  across  in  such  a  manner  as  to  block  them.  Fall  plow- 
ing is  to  be  recommended  whenever  possible  as  a  means  of  preventing  erosion. 
Only  when  the  soil  is  clayey  and  absorption  of  water  is  very  slow  will  spring 
plowing  be  advisable.  The  organic  matter  content  of  soils  should  be  kept  up  by 
the  addition  of  farm  manures,  green  manures  and  crop  residues  if  soil  subject 
to  erosion  is  to  be  properly  protected.  By  the  use  of  such  materials  the  absorb- 
ing power  of  the  soil  is  increased  and  they  also  bind  the  soil  particles  together 
and  prevent  their  washing  away  as  rapidly  as  might  otherwise  be  the  case.  By 
all  these  treatments  the  danger  of  erosion  is  considerably  reduced  and  expensive 
methods  of  control  may  be  rendered  unnecessary. 

There  are  two  types  of  erosion,  sheet  washing  and  gullying.  The  former  may 
occur  over  a  rather  large  area  and  the  surface  soil  may  be  removed  to  such  a 
large  extent  that  the  subsoil  will  be  exposed  and  crop  growth  prevented.  Sheet 
washing  often  occurs  so  slowly  that  the  farmer  is  not  aware  of  the  gradual  re- 
moval of  fertility  from  his  soil  until  it  has  actually  resulted  in  lower  crop  yields. 
Gullying  is  more  striking  in  appearance  but  it  is  less  harmful  and  it  is  usually 
more  easily  controlled.     If,  however,  a  rapidly  widening  gully  is  allowed  to 


30  SOIL  SURVEY  OF  IOWA 

grow  unchecked  an  entire  field  may  soon  be  made  useless  for  farming  purposes. 
Fields  may  be  cut  up  into  several  portions  and  the  farming  of  such  tracts  is 
more  costly  and  inconvenient.  In  Pottawattamie  county  gullying  occurs  to  an 
injurious  extent  mainly  in  the  bluffs  along  the  Missouri  River  and  a  helt  one- 
half  mile  to  three  miles  back  from  the  bluffs. 

The  means  which  may  be  employed  to  control  or  prevent  eiosion  in  Towa  may 
be  considered  under  five  headings  a.s  applicable  to  "dead  furrows,"  to  small 
gullies,  to  large  gullies,  to  bottoms,  and  to  hillside  erosion. 

EROSION  DUE  TO  DEAD  FURROWS 

Dead  furrows  or  back  furrows,  when  mnning  with  the  slope  or  at  a  consider- 
able angle  with  it,  frequently  result  in  the  formation  of  gullies. 

^'Plowing  In/' — It  is  (piite  customary  to  "plow  in"  the  small  gullies  that 
result  from  these  dead  furrows  and  in  level  areas  where  the  soil  is  deep,  this 
"plowing  in"  process  may  be  quite  effective.  In  the  more  rolling  areas,  how- 
ever, where  the  soil  is  rather  shalloAv,  the  gullies  formed  from  dead  furrows 
may  not  be  entirely  filled  up  by  "plowing  in."  Then  it  is  best  to  supplement 
the  ' '  plowing  in ' '  with  a  series  of  ' '  staked  in ' '  dams  or  earth  dams. 

"Staking  In." — The  method  of  "staking  in"  is  better  as  it  requires  less 
work  and  there  is  less  danger  of  washing  out.  The  process  consists  in  driving 
in  several  series  of  stakes  across  the  gully  and  up  the  entire  hillside  at  intervals 
of  from  15  to  50  yards,  according  to  the  slope.  The  stakes  in  each  series  should 
be  placed  three  to  four  inches  apart  and  the  tops  of  the  stakes  should  extend 
well  above  the  surrounding  land.  It  is  then  usually  advisable  to  weave  some 
brush  about  the  stakes,  allowing  the  tops  of  the  brush  to  point  up-stream. 
Additional  brush  may  also  be  placed  above  the  stakes,  with  the  tops  pointing  up- 
stream, peniiitting  the  water  to  filter  thru,  but  holding  the  fine  soil. 

Earth  Dams. — Earth  dams  consist  of  mounds  of  soil  placed  at  intervals  along 
the  slope.  They  are  made  somewhat  higher  than  the  surrounding  land  and  act 
in  much  the  same  way  as  the  stakes  used  in  the  "staking  in"  operation.  There 
are  some  objections  to  the  use  of  earth  dams,  but  in  many  cases  they  may  be 
quite  effective  in  preventing  erosion  in  "dead  furrows." 

SMALL  GULLIES 

Gullies  result  from  the  enlargement  of  surface  drainageways  and  they  may 
occur  in  cultivated  land,  on  steep  hillsides  in  grass  or  other  vegetation,  in  the 
bottomlands,  or  at  any  place  where  water  runs  over  the  surface  of  the  land. 
Small  gullies  may  be  filled  in  a  number  of  ways  but  it  is  not  practicable  to  fill 
them  by  dumping  soil  into  them,  for  an  immense  amount  of  labor  is  involved 
and  the  effect  will  not  be  permanent. 

"Staking  in." — The  simplest  method  of  controlling  small  or  moderate  sized 
gullies  and  the  one  that  gives  the  most  general  satisfaction  is  the  "staking  in" 
operation  recommended  for  the  control  of  dead  furrow  gullies.  The  stakes 
should  vary  in  size  with  the  size  of  the  gully,  as  should  also  the  size  and  quantity 
of  brush  w'oven  about  the  stakes.  A  modification  of  the  system  of  "staking  in" 
which  has  been  used  with  success  in  one  case  consists  in  using  the  brush  without 
stakes.     The  brush  is  cut  so  that  a  heavy  branch  i)ointing  downward,  is  left 


POTTAWATTAMIE  COUNTY  SOILS 


31 


Fig.   6.     Erosion   in   gully 


near  the  top.  This  heavy  branch  is  caught  between  a  fork  in  the  lowor  part  nf 
the  brush-pile,  or  hooked  over  one  of  the  main  stems  and  driven  well  into  the 
ground.  Enough  brush  is  placed  in  this  manner  to  extend  entirely  across  the 
gully,  with  the  tops  pointed  downstream  instead  of  upstream,  which  keeps  it 
from  being  washed  away  as  readily  by  the  action  of  a  large  volume  of  water 
flowirig  vipon  it.  A  series  of  these  brushpiles  may  be  installed  up  the  course  of 
the  gully  and  with  the  regular  repair  of  washouts  or  undereuttings  may  prove 
very  effective. 

The  Straw  Dam. — A  simple  method  of  preventing  erosion  in  small  gullies  is 
to  fill  them  with  straw.  This  may  be  done  at  threshing  time  with  some  saving 
of  time  and  labor.  The  straw  is  usually  piled  near  the  lower  part  of  the  gully, 
but  if  the  gully  is  rather  long  or  branching,  it  should  be  ])laced  near  the  middle 
or  below  the  junction  of  the  branches  or  more  than  one  dam  should  be  used. 
The  pile  should  be  made  so  large  that  it  will  not  wash  out  readily  when  it  gets 
smaller  thru  decomposition  and  settling.  One  great  objection  to  he  use  of  straw 
is  the  loss  of  it  as  a  feed,  as  a  bedding  material  and  as  a  fertilizer.  Yet  its  use 
may  be  warranted  on  large  farms  which  are  o])erate(l  on  an  extensive  scale  be- 
cause of  the  saving  in  time,  labor  and  inspection. 

The  Earth  Dam. — The  use  of  an  earth  dam  or  mound  of  earth  across  a  gully  may 
be  a  satisfactory  method  of  controlling  erosion  under  some  conditions.  It  will 
prove  neither  efficient  nor  permanent,  however,  unless  the  soil  above  the  dam  is 
sufficiently  open  and  porous  to  allow  of  a  rather  rapid  removal  of  water  by  di'ain- 
age  thru  the  soil.  Otherwise  too  large  amounts  of  water  may  accumulate  above 
the  dam  and  wash  it  out.     In  general  it  may  be  said  that  when  not  provided 


32  SOIL  SUEVEY  OF  IOWA 

with  a  suitable  outlet  under  the  dam  for  surplus  water  the  earth  dam  cannot 
be  recommended.  When  such  an  outlet  is  provided  the  dam  is  called  a  ' '  Chris- 
topher" or  "Dickey"  dam. 

The  "Christopher"  or  "Dickey"  Dam. — This  modification  of  the  earth  dam 
consists  merely  in  laying  a  line  of  tile  down  the  gully  and  beneath  the  dam,  an 
elbow  or  a  "T"  being  inserted  in  the  tile  just  above  the  dam.  This  "T,"  called 
the  surface  inlet,  usually  extends  two  or  three  feet  above  the  bottom  of  the  gully. 
A  large  sized  tile  should  be  used  in  order  to  provide  for  flood  waters  and  the  dam 
should  be  provided  with  a  cement  or  board  spillway  or  runoff  to  prevent  any 
cutting  back  by  the  water  flowing  from  the  tile.  The  earth  dam  should  be  made 
somewhat  higher  and  -VN^der  than  the  gully  and  higher  in  the  center  than  at  the 
sides  to  reduce  the  dangers  of  washing.  It  is  advisable  to  grow  some  crop  upon 
it,  such  as  sorghum,  or  even  oats  or  rye,  and  later  seed  it  to  grass.  Considering 
the  cost,  maintenance,  permanence,  and  efficiency,  the  Christopher  or  Dickey 
dam,  especially  when  arranged  in  series  of  two  or  more,  may  be  regarded  as  the 
best  method  of  filling  ditches  and  gullies  and  as  especially  adapted  to  the  larger 
gullies. 

The  stone  or  nibble  dam. — ^Where  stones  abound  they  are  frequently  used  in 
constructing  dams  for  the  control  of  erosion.  "With  proper  care  in  making  such 
dams  the  results  in  siiiall  gullies  may  be  quite  satisfactory,  especially  when  tile 
openings  have  been  provided  in  the  dam  at  various  heights.  The  efficiency  of 
the  stone  dam  depends  rather  definitely  upon  the  method  of  construction.  If  it 
is  laid  up  too  loosely,  its  efficiency  is  reduced  and  it  may  be  washed  out.  Such 
dams  can  be  used  only  very  infrequently  in  Iowa. 

The  rubbish  dam. — The  use  of  rubbish  in  controlling  erosion  is  a  method 
sometimes  followed  and  a  great  variety  of  materials  may  be  employed.  The 
results  are  in  the  main  rather  unsatisfactory  and  it  is  a  very  unsightly  method. 
Little  effect  in.  preventing  erosion  results  from  the  careless  use  of  rubbish  even 
if  a  sufficient  amount  is  used  to  fill  the  cut.  The  rubbish  dam  may  be  used, 
however,  when  combined  "svith  the  Dickey  system,  just  as  the  earth  dam  or 
stone  dam,  provided  it  is  made  sufficiently  compact  to  retain  sediment  and  to 
withstand  the  washing  effect  of  the  water. 

The  ivoven  wire  dam. — The  use  of  woven-wire,  especially  in  connection  with 
brush  or*rubbish,  has  sometimes  proven  satisfactory  for  preventing  erosion  in 
small  gullies.  The  woven  wire  takes  the  plaae  of  the  stakes,  the  principle  of 
construction  being  otherwise  the  same  as  in  the  "staking  in"  system.  It  can 
only  be  reconmiended  for  shallow,  fiat  ditches  and  in  general  other  methods  are 
somewhat  preferable. 

Sod  strips. — The  use  of  narrow  strips  of  sod  along  natural  surface  drainage- 
ways  may  often  prevent  these  channels  from  washing  into  gullies,  as  the  sod 
serves  to  hold  the  soil  in  place.  The  amount  of  land  lost  from  cultivation  in  this 
way  is  relatively  small  as  the  strips  are  usually  only  a  rod  or  two  in  width. 
Bluegra&s  is  the  best  crop  to  use  for  the  sod,  but  timothy,  redtop,  clover  or 
alfalfa  may  serve  quite  as  well  and  for  quick  results  sorghum  may  be  employed 
if  it  is  planted  thickly.  This  method  of  controlling  erosion  is  in  common  use 
in  certain  areas  and  it  might  be  employed  to  advantage  in  many  other  cases. 

The  concrete  dam. — One  of  the  most  effective  means  of  controlling  erosion  is  by 


POTTAWATTAMIE  COUNTY  SOILS  33 

the  concrete  dam,  provided  the  Dickey  system  is  used  in  connection  with  it. 
They  are,  however,  rather  expensive.  Then,  too,  they  may  overturn  if  not 
properly  designed  and  the  services  of  an  expert  engineer  are  required  to  insure 
a  correct  design.  Owing  to  their  high  cost  and  the  difficulty  involved  in  secur- 
ing a  correct  design  and  construction,  such  dams  cannot  be  considered  as  adapted 
to  general  use  on  the  farm. 

Drainage. — The  ready  removal  of  excess  water  may  be  accomplished  by  a 
system  of  tile  drainage  properly  installed.  This  removal  of  water  to  the  depth 
of  the  tile  increases  the  water  absorbing  power  of  the  soil,  and  thus  decreases 
the  tendency  toward  erosion.  Catch  wells  properly  located  over  the  surface 
and  consisting  of  depressions  or  holes  filled  with  coarse  gravel  and  connected 
with  the  tile  help  to  catch  and  carry  away  the  excess  water.  In  some  places 
tiling  alone  may  be  sufficient  to  control  erasion,  but  generally  other  means  are 
also  required. 

LAEGE  GULLIES 

The  erosion  in  large  gullies  which  are  often  called  ravines  may  in  general  be 
controlled  by  the  same  methods  as  in  the  case  of  small  gullies.  The  Christopher 
dam,  already  described,  may  also  serve  in  the  case  of  large  gullies.  The  pre- 
cautions to  be  observed  in  the  use  of  this  method  of  control  have  already  been 
described  and  emphasis  need  only  be  placed  here  upon  the  importance  of  carrj'- 
ing  the  tile  some  distance  down  the  gully  to  protect  it  from  washing.  The 
Dickey  dam  is  the  only  method  that  can  be  recommended  for  controlling  and 
filling  large  gullies  and  it  seems  to  be  giving  very  satisfactory  results  at  the 
present  time. 

BOTTOMLANDS 

Erosion  frequently  occurs  in  bottomlands  and  especially  where  such  low- 
lying  areas  are  crossed  by  small  streams  the  land  may  be  very  badly  cut  up  and 
rendered  almost  entirely  valueless  for  farming  purposes. 

Straightening  and  tiling. — The  straightening  of  the  larger  streams  in  bottom 
land  areas  may  be  accomplished  by  any  community  and  while  the  cost  is  con- 
siderable, large  areas  of  land  may  thus  be  reclaimed.  In  the  case  of  small 
streams,  tiling  may  be  the  only  method  necessary  for  reclaiming  useless  bottom 
land  and  it  often  proves  very  efficient. 

Trees. — Erosion  is  sometimes  controlled  hy  rows  of  such  trees  as  willows 
which  extend  up  the  drainage  channels.  While  the  method  has  some  good 
features  it  is  not  generally  desirable.  The  row  of  trees  often  extends  much 
further  into  cultivated  areas  than  is  necessary  and  tillage  operations  are  inter- 
fered with.  Furthermore,  the  trees  may  seriously  injure  the  crops  in  their  im- 
mediate vicinity  because  of  their  shade  and  because  of  the  water  which  they 
remove  from  the  soil.  In  general  it  may  be  said  that  in  pastures,  bottomlands 
and  gulches  the  presence  of  trees  may  be  quite  effective  in  controlling  erosion, 
but  a  row  of  trees  across  cultivated  land  or  even  extending  out  into  it,  cannot 

be  recommended. 

HILLSIDE  EROSION 

Hillside  erosion  may  be  controlled  by  certain  methods  of  soil  treatment  which 
are  of  value,  not  only  in  preventing  the  injurious  washing  of  soils,  but  in  aiding 
materially  in  securing  satisfactory  crop  growth. 


34  SOIL  SURVEY  OF  IOWA 

Use  of  organic  mottrr. — Organic  matter  or  Iniiuus  is  the  most  effective  means 
of  increasing  the  absorbing  power  of  the  soil  and  hence  it  proves  very  effective 
in  preventing  erosion.  Farm  manure  may  be  used  for  this  purpose  or  green 
manures  may  be  employed  if  farm  manure  is  not  available  in  sufficient  'amounts. 
Crop  residues  such  as  straw,  corn  stalks,  etc.,  may  also  be  turned  under  in  soils 
to  increase  their  organic  matter  content.  In  general  it  may  be  said  that  all 
means  which  may  be  employed  to  increase  the  organic  matter  content  of  soils 
will  have  an  important  influence  in  preventing  erosion. 

Growing  of  crops. — The  growing  of  crops,  such  as  alfalfa,  that  remain  on  the 
land  continuously  for  a  period  of  two  or  more  years  is  often  advisable  on  steep 
hillsides.  Alsike  clover,  sweet  clover,  timothy  and  red  top  are  also  (|uite  neces- 
sary for  use  in  such  locations.  The  root  system  of  such  crops  as  these  holds  the 
soil  together  and  the  washing  action  of  rainfall  is  reduced  to  a  nuirked  extent. 

Contour  discing. — Discing  around  a  hill  instead  of  up  and  down  the  slope  or 
at  an  angle  to  it  is  fre(iuently  very  effective  in  preventing  erosion.  This  prac- 
tice is  "called  "contour  discing"  and  it  has  proven  quite  satisfactory  in  many 
cases  in  Iowa.  Contour  discing  is  practiced  to  advantage  on  stalk  ground  in 
the  spring,  preparatory  to  seeding  small  grain,  and  also  on  fall  plowed  land 
that  is  tobe  planted  to  corn.  It  is  advisable  in  contour  discing  to  do  the  turning 
row  along  the  fence,  up  the  slope,  first  as  the  horses  and  disc  when  turning  will 
pack  and  cover  the  center  mark  of  the  disc,  thus  leaving  no  de{)rehsion  to  foim  a 
water  channel. 

Deep  plowing. — Deep  plowing  increases  the  absorptive  power  of  the  soil  and 
hence  decreases  erosion.  It  is  especially  advantageous  if  it  is  done  in  the  fall 
as  the  soil  is  then  put  in  condition  to  al)sorb  and  hold  the  largest  possible  amount 
cf  the  late  fall  and  early  spring  rains.  It  is  not  advisable,  however,  to  change 
from  shallow  plowing  to  deep  plowing  at  a  single  operation  as  too  much  subsoil 
may  be  mixed  with  the  surface  soil  and  the  productive  power  of  the  soil  there- 
fore reduced.  A  gradual  deepening  of  the  surface  soil  by  increasing  the  depth 
of  plowing  will  be  of  value  both  in  increasing  the  feeding  zone  of  plant  roots: 
tind  in  making  the  soil  more  absorptive  and  therefore  less  subject  to  erosion. 

INDIVIDUAL  SOIL  TYPES  IN  POTTAWATTAMIE  COUNTY* 

LOESS  SOILS 

There  are  two  soil  areas  in  Pottawattamie  county  which  are  classed  as  loess 

soils,  the  Marshall  silt  loam  and  the  Knox  silt  loam.     These  two  types  cover 

over  72  per  cent  of  the  area  of  the  county  and  constitute,  therefore,  the  most 

important  soils 

MARSHALL  SILT  LOAM   (9) 

This  soil  type  covers  68  per  cent  of  the  area  of  Pottawattamie  county.  In 
depth,  the  surface  soil  ranges  from  10  to  24  inches,  while  the  subsoil  extends 
to  a  depth  of  10  to  20  feet  in  the  more  shallow  deposits,  and  from  20  to  80  feet 
in  the  more  fully  developed  deposits.  When  wet  the  surface  soil  is  a  solid 
black;  near  the  line  between  the  ^oil  and  subsoil  the  color  becomes  lighter  and 

*  Tlie  (lescri])tions  of  individual  soil  types  ^iven  in  the  Bureau  of  Soils  report  on  Pottawat- 
tamie county,  Iowa,  have  been  rather  closely  followed  in  this  section  of  the  report. 


POTTAWATTAMIE  COUNTY  SOILS  35 

sometimes  a  mottling  of  yellow,  gray  or  drab  is  found.  When  timbered  the 
soil  is  lighter  in  color  than  where  it  is  in  prairie.  Only  in  a  few  cases,  at  the 
base  of  high  hills,  is  there  any  occurrence  of  gravel  or  sandy  material.  Lime 
concretions  are  found  in  the  subsoil.  These  vary  in  size  from  one-half  inch 
to  six  inches  in  diam«4er  and  in  some  localities  occur  in  considerable  numbers. 
In  other  cases,  as  has  been  noted,  they  are  absent  and  the  soil  type  is  acid. 

The  topography  of  this  soil  is  nearly  level  to  undulating,  rolling,  or  hilly. 
It  occupies  an  elevation  thruout  the  county  ranging  from  1,000  to  1,200  feet 
above  sea  level.  The  natural  drainage  is  very  thoro.  The  streams  have  often 
cut  deep  channels  and  some  bad  cases  of  erosion  are  found  on  these  hill  slopes. 

General  farm  crops  such  as  corn,  oats,  and  wheat  produce  satisfactory  yields 
on  this  soil  and  they  are  the  principal  crops  grown.  The  average  yields  of  these 
crops  are  greater  on  this  type  than  for  the  county  as  a  whole,  indicating  quite 
distinctly  their  adaptation  to  this  soil.  Alfalfa  is  particularly  well  suited  to 
this  soil  and  it  is  being  grown  on  rapidly  increasing  areas.  Other  legumes, 
such  as  red  clover  and  sweet  clover,  also  do  well.  The  production  of  grapes 
and  apples  is  unusually  good  on  this  type  and  the  number  of  vineyards  and 
orchards  is  becoming  greater  as  the  value  of  these  crops  is  recognized.  Veg- 
etables, such  as  tomatoes,  potatoes,  beans,  cabbage,  eggplant,  beets,  turnips, 
and  parsnips,  grow  well  on  this  soil  but  they  are  not  cultivated  to  any  consid- 
erable extent  for  marketing. 

The  chief  need  of  this  soil  type,  as  has  been  pointed  out  in  the  previous  pages, 
is  for  organic  matter.  The  greenhouse  and  field  experiments  have  shown  irn- 
usually  large  effects  from  the  application  of  farm  manure.  This  material  ap- 
parently supplies  the  conditions  which  are  necessary  in  this  soil  for  the  best 
growth  of  crops.  Lime  is  sometimes  necessary,  as  in  many  instances  the  orig- 
inal content  has  been  completely  lost  by  leaching,  and  tests  should  always  be 
carefully  made  for  acidity.  Conrmercial  fertilizers  seem  to  be  unnecessary  at 
the  present  time.  Phosphorus,  however,  is  low  in  the  soil  and  applications 
show  slight  increases.  This  leads  to  the  conclusion  that  this  element  will  be 
necessary  in  the  more  or  less  distant  futirre.  Oi-ganic  matter,  however,  either 
as  farm  manure  or  as  green  manures,  seems  to  be  the  best  material  to  be  applied 
to  the  soil  at  the  present  time  and  the  results  secured  with  the  irse  of  these 
substances  show  thenr  to  be  of  economic  value. 

KNOX  SILT  LOAM   (11) 

This  soil  covers  -4.7  per  cent  of  the  area  of  the  county.  The  surface  soil  ex- 
tends to  a  depth  of  15  to  20  inches  where  it  grades  into  a  light-brown  to  buff- 
colored  silt  loam.  There  is  no  sharp  line  of  separation  between  the  surface 
soil  and  subsoil,  the  yellowish-browu  soil  gradually  merging  into  the  yellow 
subsoil.  In  some  places  the  surface  soil  is  somewhat  darker  than  the  true  soil 
type  and  resembles  more  nearly  the  ^Marshall  silt  loam. 

The  texture  of  the  soil  is  practically  a  silt  loam  to  a  depth  of  10  to  oO  feet, 
only  a  small  quantity  of  clayey  or  sandy  material  being  encountered  within  the 
3-foot  soil  section.  Sand  and  stones  are  normally  absent.  In  local  areas,  how- 
ever, where  there  has  been  some  wash  from  other  soils  there  is  occasionally  a 
little  sand. 


36  SOIL  SURVEY  OF  IOWA 

This  soil  type  occurs  in  a  narrow  strip  bordering  the  lowlands  of  the  Missouri 
river  and  is  characterized  by  steep  bluffs  and  a  generally  rough  topography. 
The  bluffs  rise  100  to  150  feet  above  the  lowlands.  The  drainage  is  normally 
good ;  in  places  where  there  are  steep,  unprotected  slopes,  it  is  excessive.  ]\Iany 
gulches  or  drainage  ways  occur  in  the  bluff  section,  and  the  slopes  leading  to 
stream  channels  are  frequently  so  steep  as  to  prohibit  cultivation. 

This  soil  is  especially  adapted  for  the  production  of  grapes  and  many  large 
vineyards  are  found  on  it.  The  steep  slopes  on  which  it  occurs  can  be  utilized 
very  satisfactorily  for  vineyards  when  other  crops  do  not  do  well.  Practically 
all  the  grape  gromng  in  the  county  occurred  on  this  soil  a  few  years  ago,  but 
now  the  Marshall  silt  loam  is  also  being  used  for  this  crop.  With  the  better 
methods  of  soil  treatment,  pruning,  etc.,  which  are  being  followed,  grapes  are 
becoming  a  more  and  more  valuable  crop.  On  the  more  level  slopes,  the  ordi- 
nary farm  crops  and  many  vegetables  do  well  on  this  soil.  Orcharding  is  also 
profitable  and  the  growing  of  apples  and  other  fruits  is  increasing. 

This  soil  is  especially  deficient  in  organic  matter,  and  it  therefore  is  in  need 
of  farm  yard  manure  and  green  manure  crops.  It  is  not  generally  acid  and  is 
not  in  striking  need  of  phosphorus,  but  the  latter  element  will  soon  be  neces- 
sary. The  chief  needs  of  this  type  to  make  it  more  productive  are  the  use  of 
methods  to  prevent  erosion  which  is  so  often  extensive  and  the  abundant  appli- 
cation of  farmyard  manure  or  the  turning  under  of  green  manure  crops. 

TERRACE  SOILS 

There  are  three  terrace  soils  in  Pottawattamie  county  included  in  the  Han- 
cock series  and  the  Osgood  series.  These  three  types  are  all  of  minor  import- 
ance in  the  county,  covering  only  3.3  per  cent  of  the  total  area. 

HANCOCK  SILT  LOAM  (23) 

This  terrace  soil  is  a  second  bottom  soil  bordering  the  overflowed  bottoms  of 
some  of  the  main  drainage  ways  of  the  county,  especially  the  East  and  West 
Nishnabotna  rivers  and  the  creeks.  The  surface  soil  extends  to  a  depth  of  12  to 
15  inches,  grading  into  a  lighter  subsoil  from  Chocolate  brown  to  mottled  yel- 
lowish-brown and  gray,  and  ranging  in  texture  from  a  silt  loam  to  a  silty  clay 
loam.  In  some  places  layers  of  very  fine  sandy  material  are  found.  Evidence 
is  frequently  found  of  the  alluvial  nature  of  this  soil,  but  it  also  receives  the 
wash  from  the  surrounding  soil  and  is  somewhat  variable  in  composition. 

This  type  is  almost  level,  sloping  gently  toward  the  streams  in  some  cases. 
In  general  it  is  very  well  drained,  but  the  water  may  stand  in  level  areas  and 
in  depressions  after  heavy  rains  and  in  such  cases  artificial  drainage  is  re- 
quired. 

Com  is  grown  the  most  extensively  of  any  crop  on  this  soil  and  its  value  is 
the  greatest.  Wheat  is  also  grown  to  a  considerable  extent  and  produces  satis- 
factory yields.  Other  crops  such  as  alfalfa,  clover,  timothy  and  rape,  and 
truck  crops  such  as  cabbage,  tomatoes,  squash,  beans,  potatoes,  etc.,  do  well  but 
they  are  not  grown  in  any  large  quantities. 

This  soil  is  not  so  low  in  organic  matter  as  the  loess  soils,  but  it  will  respond 
to  applications  of  farmyard  manure,  and  these  should  therefore  be  made.    Drain- 


POTTAWATTAMIE  COUNTY  SOILS 


37 


lir" 


i"y' m^'  y»yy  >i 


^ 


>!;i       ^^^-j** 


•H  -+H   — 


S'^o 

CC    d    !D 

=!    O  -ti 

-r*^  3 

O    <B 
O    C 

w)3  ° 

>   o   =^ 
— 1    a;   o 

o 

Ss.-S^ 

:^-E 

S  o 

c  >, « 

ci 

03    <« 

r-  «      r- 


38 


SOIL  SURVEY  OF  IOWA 


Il>; 


>rf. 


aj  _C  _2  •;-  -I-'  *j  i-  .- 

^;    ^     O     -    ^     .  ■-                     _                             X'            _ 

OC    «    O)    pi    o  -^'  S       "x    .^  .      ^          X 

a6o«-^g  o§      ^f  r-a  -^^      -i® 


.•     t-     O  HH 

[B     !«  .-I    -I-    -1-         "' 


Oi 


POTTAWATTAMIK  COUNTY  SOILS  39 

age  of  some  areas  is  necessary'  and  the  use  of  phosphorus  may  be  required  in 
the  near  future.     Lime  is  not  necessary  at  the  present  time. 

HANCOCK  SILTY  CLAY^   (24) 

This  soil  is  a  minor  type  in  Pottawnttainie  county.  The  surface  soil  is 
only  4  to  6  inches  in  depth,  and  the  subsoil  extends  to  12  to  15  inches,  giving 
way  below  to  a  gray  and  brown  mottled  or  drab  heavy  plastic  clay  which  ex- 
tends to  three  feet  or  more. 

The  topography  of  this  soil  is  level,  a  gentle  slope  toward  the  river  being 
noticeable,  llnderdrainage  is  generally  well  established,  but  in  some  ca>-es  the 
water  stands  in  depressions  and  makes  the  soil  slippery  and  muddy. 

Corn,  alfalfa  and  truck  crops,  such  as  beets,  tomatoes,  cabbage,  potatoes  and 
beans  give  good  yields  on  this  soil,  corn  and  alfalfa  being  especially  valuable. 

The  needs  of  this  soil,  apart  from  diaina^e  which  is  the  first  essential,  include 
the  use  of  organic  matter  and  phosi)liorus  altho  neither  of  these  materials  is 
so  necessary  as  on  the  loess  soils  or  the  other  terrace  types. 

OSGOOD  VERY  FINE   SAND    (25) 

This  type  is  mapped  only  in  four  very  small  areas  near  the  Missouri  river, 
west  and  south  of  Council  Bluffs.  The  surface  soil  extends  to  12  to  15  inclies 
and  grades  into  the  lighter  subsoil  of  the  same  texture  throughout  the  3-foot 
section. 

It  is  almost  level  in  topography  and  possesses  a  very  loose  structure,  hence 
the  drainage  is  excessive.  Crops  are  apt  to  suffer  for  moisture  on  this  soil  dur- 
ing dry  seasons. 

It  is  very  low  in  organic  matter  and  hence  its  chief  need  is  for  farm  yard 
manure  or  green  manure  crops.  These  materials  would  not  only  provide  better 
mechanical  soil  conditions,  preventing  the  rapid  drying  out,  but  they  would 
supply  plant  food  and  enable  proper  decomposition  processes  to  occur.  These 
materials  together  with  phosphorus  fertilizers  which  will  undoubtedly  be  nec- 
essary in  the  near  future  will  make  this  soil  type  more  productive.  It  is  an 
extreme  type  and  of  small  occurrence,  but  it  is  worth  special  effort  to  make  it 
fertile. 

When  well  fertilized,  early  truck  crops,  melons  and  cantaloupes  can  profitably 
be  grown  on  this  soil.  General  farm  crops  such  as  corn  nuiy  also  be  grown 
satisfactorily. 

SWAMP  AND  BOTTOMLAND  SOILS 

Five  tj^pes  of  soil  are  included  in  the  group  of  swamp  and  bottomland  soils. 
The  total  area  covered  by  them  is  24  per  cent  of  the  area  of  the  county,  and  in- 
cludes the  Wabash  and  Sarpy  soils. 

WABASH  SILT  LOAM  (26) 

This  soil  type  covers  over  13  per  cent  of  the  area  of  Pottawattamie  county 
and  it  is  largely  developed  thruout  the  county  along  the  overflowed  bottoms  of 
Walnut  and  Pigeon  creeks. 

The  surface  soil  of  this  type,  which  grades  from  a  dark-brown  to  almost 
black  mellow  silt  loam,  ranges  from  8  to  15  inches  in  depth  and  in  places  ex- 


40  SOIL  SURVEY  OF  IOWA 

tends  as  deep  as  25  inches.  The  subsoil  is  lighter  in  color,  varying  from  a  light- 
brown  to  mottled  yellow  and  gray  heavy  silt  loam.  Pockets  of  sand  occur  in 
places. 

The  topography  of  this  type  is  almost  level.  It  occupies  the  first  bottoms 
and  is  therefore  subject  to  overflow  at  least  in  part.  The  type  as  a  whole  suf- 
fers considerably  from  erosion,  especially  those  portions  adjoining  the  streams. 
Frequently  rather  considerable  areas  are  removed  from  one  place  to  another. 
Straightening  the  channels  of  the  streams  is  the  best  way  to  protect  the  land. 
The  portions  of  the  soil  near  the  uplands  adjoining  the  terrace  soils  are  fairly 
well  drained,  while  the  lower  flat  areas  are  of  course  poorly  drained.  The 
deepening  of  the  streams  by  dredging  will  lower  the  water  level  and  make 
these  flat  areas  more  productive  and  the  crop  less  liable  to  be  flooded  out. 

Corn  is  the  most  important  crop  grown  on  this  soil.  Oats  and  other  farm 
crops  which  can  be  planted  and  harvested  the  same  season  also  do  well.  Winter 
wheat  or  long  season  crops  are  liable  to  injury  from  drowming  out,  or  from 
the  heaving  of  the  land  under  the  action  of  the  winter  freezes.  Much  of  the 
type  is  seeded  to  grass  and  makes  an  excellent  pasture.  Alfalfa  can  be  grown 
provided  the  stream  channels  are  straightened  and  the  water  level  lowered  to  at 
lea^  5  feet  below  the  surface.  The  low  lying  parts  of  this  soil  are  allowed  to 
grow  up  to  native  grasses  and  serve  as  pasture  land. 

The  Wabash  silt  loam  is  fairly  well  supplied  with  plant  food,  but  like  the 
other  soils  in  the  county  it  is  rather  low  in  organic  matter  and  phosphorus  and 
these  are  the  constituents  which  are  necessary  to  make  it  fertile.  That  is,  after 
the  soils  have  been  protected  from  flooding,  the  next  requisite  is  the  use  of  farm 
manure  or  green  manures,  preferably  the  former,  to  start  the  proper  decomposi- 
tion processes  and  supply  the  best  physical  conditions.  Phosphorus  will  be 
necessary  in  the  near  future  for  the  phosphorus  content  is  so  low  that  crops 
will  soon  be  in  need  of  that  element.  Lime  is  not  necessary  in  general  at  the 
present  time,  but  it  probably  will  be  required  in  a  short  time  on  this  soil  when 
under  intensive  cultivation.  With  these  treatments,  crop  production  should  be 
very  satisfactory  and  the  permanent  fertility  of  the  soil  should  be  maintained. 

WABASH  SILT  LOAM  (COLLUVIAL  PHASE)    (26a) 

(This  type  is  indicated  on  the  map  by  number  26,  but  is  shown  in  a  darker  color  than  the 
typical  Wabash  silt  loam.) 

This  soil  type  occurs  thruout  the  county  in  a  narrow  strip  of  alluvial  and 
colluvial  material  along  the  minor  streams  and  drainage  ways.  This  material 
also  occurs  on  the  outer  edge  of  the  lowlands  along  nearly  all  the  larger  streams, 
but  the  areas  are  in  many  cases  too  narrow  to  be  shown  on  the  map.  The  color 
of  the  soil  is  practically  the  same  as  that  of  the  true  Wabash  silt  loam  and  it  is 
somewhat  similar  in  other  characteristics.  In  many  places  it  is  flooded  at 
periods  of  heavy  rainfall,  but  as  it  occurs  on  steep  slopes  the  surplus  water 
runs  off  quite  rapidly  and  in  general  it  may  be  said  that  it  is  not  in  need  of 
drainage.     In  this  respect,  therefore,  it  differs  from  the  Wabash  silt  loam. 

Practically  all  the  crops  grown  in  the  county  seem  to  do  well  on  this  phase. 
Com  is  the  most  important  crop,  both  in  acreage  and  production.  Wheat,  oats, 
rye,  barley,  alfalfa,  timothy,  clover  and  small  truck  crops  are  also  grown  ex- 


POTTAWATTAMIE  COUNTY  SOILS  41 

tensively.  Oats  and  spring  wheat  do  not  usually  do  as  Avell  as  on  the  upland 
soils  but  the  yields  of  some  of  the  other  crops  mentioned  are  frequently  quite 
as  satisfactory  as  on  the  better  types  of  soil.  Much  of  the  phase  which  lies  above 
overflow  is  seeded  to  alfalfa,  red  clover  and  rape,  all  of  which  do  well.  The 
low-lying  portions  are  often  allowed  to  grow  up  to  native  grasses  and  used  for 
pasture. 

The  varying  conditions  under  which  this  type  occurs  with  respect  to  overflow, 
drainage,  and  general  location,  make  it  exceedingly  variable  in  value  and  the 
land  sells  for  $75  to  $150  per  acre. 

In  chemical  composition,  the  soil  is  practically  the  same  as  the  main  type 
and  hence  its  needs  are  very  similar.  It  is  quite  low  in  organic  matter  and 
phosphorus  and  it  should  receive  applications  of  farm  manure  and  green  manures 
in  order  to  bviild  it  up  in  humus,  and  in  the  near  future  phosphorus  fertilizers 
must  be  used.  With  these  treatments  and  the  application  of  lime,  if  found 
necessary  in  special  cases,  this  soil  can  be  made  very  productive  and  kept  so, 
provided  of  course  it  is  protected  from  flooding. 

WABASH  SILTY  CLAY   (27) 

This  soil  covers  about  8  per  cent  of  the  area  of  the  county.  It  is  also  locally 
kno\ATi  as  "gumbo."  It  occupies  level  or  depressed  areas  within  the  broader 
bottomlands,  and  is  typically  developed  along  the  first  bottoms  of  the  East 
and  West  Nishnabotna  rivers  and  along  the  Missouri  river,  lying  somewhat 
back  from  the  main  stream  channel. 

The  surface  soil  extends  to  a  depth  of  4  to  6  inches  and  rests  on  a  heavy, 
stiff,  sticky,  plastic  clay,  bluish  gray  or  drab  to  gray  and  brown  mottled  in 
color.  The  surface  soil  when  wet  becomes  slippery  and  on  drying  cracks  and 
separates  into  irregular  cakes  or  blocks.  In  places  fine  sand  is  mixed  with  the 
clay,  lying  between  two  layers  of  heavy  clay. 

It  is  subject  to  overflow,  but  the  larger  portion  of  the  type  is  quite  suitable 
for  agricultural  purposes  when  well  drained.  The  lower  depressions  and  old 
lake  beds  retain  excessive  amounts  of  moisture  and  cannot  be  cultivated.  Even 
protected  areas  are  apt  to  be  covered  during  freshets,  the  water  covering  the 
soil  until  after  planting  time.  Very  little  tile  drainage  has  been  done  and  the 
cost  is  great.  The  proper  drainage  of  the  soil  is,  however,  the  prime  essential 
for  the  preparation  of  the  soil  for  crop  gro\\i:h  and  the  cost  involved  is  more 
than  offset  by  the  returns  secured.  Wlien  this  is  accomplished,  proper  cultiva- 
tion and  treatment  will  make  the  soil  very  productive,  provided  of  course,  that 
the  rainfall  is  not  so  heavy  that  the  soil  is  flooded.  The  time  of  plowing  is 
very  important.  The  soil  should  neither  be  too  wet  nor  too  dry  when  plowed 
or  it  will  be  lumpy  and  difficult  to  cultivate. 

The  addition  of  farm  manure  and  green  manures  would  prove  of  value  on 
this  soil.  Phosphorus  will  be  required  and  may  be  necessary  now,  and  lime 
while  not  needed  at  the  present  time,  must  be  used  sooner  or  later.  Proper 
drainage  and  fall  plowing  have  been  found  to  be  very  effective  in  making  this 
"gumbo"  soil  productive.  Under  such  treatment  land  of  little  value  may  be 
made  equal  in  value  to  the  best  land  in  the  state.  Com  is  the  principal  crop 
gro\^^l  on  this  soil,  and  gives  satisfactory  yields.     Oats,  spring  wheat  and  al- 


42  SOIL  SURVEY  OF  IOWA 

falfa  also  do  well  altho  the  small  grains  often  grow  so  rank  that  tliey  lodge. 
Bluegrass  is  growTi  on  the  lower  more  poorly  drained  areas  and  the  pastures 
are  used  for  fattening  beef  cattle. 

SABPY  VERY  FINE  SANDY  LOAM  (28) 

This  soil  type  is  of  minor  impoi'tance  in  Pottawattamie  eonnty,  covering  only 
1.8%  of  its  area.  It  is  usually  associated  with  the  Wabash  silty  clay  just  de- 
scribed, but  it  occupies  a  somewhat  higher  elevation  above  the  main  channel 
of  the  river. 

The  surface  soil  is  10  to  15  inches  deep  and  varies  from  a  light-brownis«h 
gray  to  grayish-brown  veiy  fine  sandy  loam  and  the  subsoil  is  very  similar  in 
color,  but  is  generally  more  open  in  structure  and  coarser  in  texture.  The 
percentage  of  sand  increases  with  the  depth,  the  soil  often  grading  into  a  fine 
sand  at  a  depth  of  thirt.y-six  inches  or  more. 

The  topography  is  level  to  slightly  undulating,  with  occasional  sandy  ridges. 
The  drainage  is  good.  Like  the  other  bottomland  soils,  this  type  is  subject  to 
overflow  and  there  is  danger  of  floods  during  the  growing  sea.son,  causing  loss 
of  crops. 

Com  is  the  main  crop  grown  on  this  soil  and  the  yields  are  quite  satisfactory. 
Wheat,  oats,  timothy,  clover  and  alfalfa  are  grown  to  a  small  extent.  Alfalfa 
gives  good  yields  but  is  apt  to  be  drowned  out  by  flood  waters.  Truck  crops 
such  as  sweet  potatoes,  Irish  potatoes,  cabbage,  melons  and  cantaloupes  are 
being  grown  in  increasing  quantities  and  are  proving  quite  profitable.  The  use 
of  the  soil  for  pasture  crops  is  also  profitable. 

The  main  need  of  this  soil  type  is  for  organic  matter.  It  is  particularly  de- 
ficient in  this  material  and  should  receive  heavy  applications  of  farmyard 
manure.  Green  manure  crops  should  also  be  used  in  addition  to  the  farm 
manure  to  supply  the  necessary  organic  matter. 

Phosphorus  is  also  necessary  or  will  soon  be  required,  and  lime  must  un- 
doubtedly be  used  in  the  near  future.  With  the  proper  supply  of  organic  mat- 
ter and  phosphorus  and  lime  the  soil  can  be  made  very  fertile  and  kept  so. 

SARPY  VERY  FINE  SAND   (29) 

This  soil  type  is  of  extremely  minor  importance,  covering  only  0.4%  of  the 
total  area  of  the  county.  There  are  a  few  small  areas  along  the  old  channels 
of  the  ]\rissouri  river,  occurring  as  long,  narrow  ridges,  and  also  in  the  flood 
plains  adjoining  the  river.  These  fine  sands  are  easily  moved  by  the  wind  and 
are  constantly  shifting.  The  surface  soil  occurs  to  a  depth  of  10  to  15  inches 
and  grades  into  a  darker  colored  sand,  the  texture  remaining  the  same,  through 
the  three-foot  section. 

The  topography  of  these  sand  areas  is  level  to  gently  undulating,  altho  in  a 
few  places  small  sand  dunes  have  been  found.  Corn,  watermelons  and  canta- 
loupes are  the  principal  crops  grown  on  this  soil.  Corn  does  only  fairly  well, 
but  melons  prove  quite  profitable.     The  chief  use  of  this  soil  is  for  pasture. 

The  soil  is  so  loose  and  open  in  texture  that  the  drainage  is  excessive.  The 
chief  need  of  this  soil  type  therefore  is  the  use  of  humus-forming  materials  to 
improve  the  physical,  chemical  and  bacteriological  conditions  in  the  soil.    Farm- 


POTTAWATTAMIE  COUNTY  SOILS 


43 


3t 


31  B 


v^^ivi^llW 


i.^x  i.^-  4 


1^ 


\ 


1 ,  29  B  »^^  •":*  :'-..  nil  3°  B  i_- 


F\iy.  9.     SuitMco,  siihsuii'ace  and  subsoils  of  tliree  of  the  individual  soil  types  of  I'ottawatta- 

niie  county 

31.     Sarpy   very   line   sandy  loam  29.     Knox  silt  loam  :w.     Marshall  silt  loam 

yard  manure  will  sen-o  this  purpose,  but  leguminous  green  manures  have  lieen 
found  on  similar  soils  to  be  particularly  efficient  in  building  them  up  and  mak- 
ing them  productive.  Such  green  manures  not  only  «upply  organic  nuitter,  but 
also  nitrogen  and  are,  therefore,  doul)ly  efficient.  Phosphorus  is  also  lacking 
in  this  soil  and  should  be  applied  if  satisfactory  yields  are  to  be  secured.  Lime 
is  not  necessary  at  the  present  time,  but  undoubtedly  will  be  in  the  near  future. 
When  proper  'methods  of  ti'eatment  are  followed  and  satisfactory  crop  yields 
are  secured,  this  material  will  soon  bccouit  deficiuit  and  will  need  to  be  sup- 
plied. Such  light  soils  can  be  built  up  into  a  satisfactory  state  of  fertility 
and  maintained  so  if  the  above  methods  of  treatment  are  carefullv  cari'ied  out. 


I 


APPENDIX 

THE  SOIL  SURVEY  OF  IOWA 

What  soils  need  to  make  them  highly  productive  and  to  keep  them  so,  and  how  their  needs 
may  be  supplied  are  problems  which  are  met  constantly  on  the  farm  today. 

To  enable  every  Iowa  farmer  to  solve  these  problems  for  his  local  conditions,  a  complete 
survey  and  study  of  the  soils  of  the  state  has  been  undertaken,  the  results  of  which  will  be 
published  in  a  series  of  county  reports.  This  work  includes  a  detailed  survey  of  the  soils  of 
each  county,  following  which  all  the  soil  types,  streams,  roads,  railroads,  etc.,  are  accurately 
located  on  a  soil  map.  This  portion  of  the  work  is  being  carried  ou  in  cooperation  with  the 
Bureau  of  Soils  of  the  United  States  Department  of  Agriculture. 

Samples  of  soils  are  taken  and  examined  mechanically  and  chemically  to  determine  their 
character  and  composition  and  to  learn  their  needs.  Pot  experiments  with  these  samples  are 
conducted  in  the  greenhouse  to  ascertain  the  value  of  the  use  of  manure,  fertilizers,  lime  and 
other  materials  on  the  various  soils.  These  pot  tests  are  followed  in  many  cases  by  field 
experiments  to  check  the  results  secured  in  the  greenhouse.  The  meagerness  of  the  funds 
available  for  such  work  has  limited  the  extent  of  these  field  studies  and  tests  have  not  been 
possible  in  each  county  surveyed.  Fairly  complete  results  have  been  secured,  however,  on 
the  main  soil  types  in  the  large  soil  areas. 

Following  the  survej^,  systems  of  soil  management  which  should  be  adopted  in  the  various 
counties  and  on  the  different  soils  are  worked  out,  old  methods  of  treatment  are  emphasized 
as  necessary  or  their  discontinuance  advised,  and  new  methods  of  proven  value  are  suggested. 
The  published  reports  as  a  whole  will  outline  the  methods  which  the  farmers  of  the  state  must 
employ  if  they  wish  to  maintain  the  fertility  of  their  soils  and  insure  the  best  crop  produc- 
tion. 

The  various  counties  of  the  state  will  be  surveyed  as  rapidly  as  funds  will  permit,  the 
number  included  each  year  being  determined  entirely  by  the  size  of  the  appropriation  avail- 
able for  the  work.  The  order  in  which  individual  counties  will  be  chosen  depends  very 
largely  upon  the  interest  and  demand  in  the  county  for  the  work.  Petitions  signed  by  the 
residents,  and  especially  by  the  farmers  or  farmers'  organizations  of  the  county,  should  be 
submitted  to  indicate  the  sentiment  favorable  to  the  undertaking.  Such  petitions  are  filed 
in  the  order  of  their  receipt  and  aid  materially  in  the  annual  selection  of  counties. 

The  reports  giving  complete  results  of  the  surveys  and  soil  studies  in  the  various  counties 
will  be  published  in  a  special  series  of  bulletins,  as  rapidly  as  the  work  is  completed.  Some 
general  information  regarding  the  principles  of  permanent  soil  fertility  and  the  character, 
needs  and  treatment  of  Iowa  soils,  gathered  from  various  published  and  unpublished  data 
accumulated  in  less  specific  experimental  work  will  be  included  in  or  appended  to  all  the 
reports. 

PLANT  FOOD  IN  SOILS 

Fifteen  different  chemical  elements  are  essential  for  plant  food,  but  many  of  these  occur 
so  extensively  in  soils  and  are  used  in  such  small  quantities  that  there  is  practically  no 
danger  of  their  ever  running  out.  Such,  for  example,  is  the  case  with  iron  and  aluminum, 
past  experience  showing  that  the  amount  of  these  elements  in  the  soil  remains  practfically 
constant. 

Furthermore,  there  can  never  be  a  shortage  in  the  elements  which  come  primarily  from  the 
air,  such  as  carbon  and  oxygen,  for  the  supply  of  these  in  the  atmosphere  is  practically  in- 
exhaustible. The  same  is  true  of  nitrogen,  wliich  is  now  known  to  be  taken  directly  from 
the  atmosphere  by  well-inoculated  legumes  and  by  certain  microscopic  organisms.  Hence, 
altho  many  crops  are  unable  to  secure  nitrogen  from  the  air  and  are  forced  to  draw  on  the 
soil  supply,  it  is  possible  by  the  proper  and  frequent  growing  of  well-inoculated  legumes  and 
their  use  as  green  manures,  to  store  up  sufficient  of  this  element  to  supply  all  the  needs  of 
succeeding  non-legumes. 

Knowledge  of  the  nitrogen  content  of  soils  is  important  in  showing  whether  sufficient  green 


46 


SOIL  SURVEY  OF  IOWA 


Fig.   10.     Map  of  Iowa  showing  the  counties  surveyed 


manure  or  barnyard  manure  has  been  applied  to  the  soil.  Commercial  nitrogenous  fertilizers 
are  now  known  to  be  unnecessary  where  the  soil  is  not  abnormal,  and  green  manures  may  be 
used  in  practically  all  cases.  Where  a  crop  must  be  "forced,"  as  in  market  gardening,  some 
nitrogenous  fertilizer  may  be  of  value. 

THE    "SOIL   DERIVED"    ELEMENTS 

Phosphorus,  potassium,  calcium  and  sulfur,  known  as  "soil-derived"  elements,  may  fre- 
quently be  lacking  in  soils,  and  then  a  fertilizing  material  carrying  the  necessary  element  must 
be  used.  Phosphorus  is  the  element  most  likely  to  be  deficient  in  all  soils.  This  is  especially 
true  in  Iowa  soils.  Potassium  frequently  is  lacking  in  peats  and  swampy  soils,  but  normal  soils 
in  Iowa  and  elsewhere  are  usually  well  supplied  with  this  element.  Calcium  may  be  low  in 
soils  which  have  borne  a  heavy  growth  of  a  legume,  especially  alfalfa;  but  a  shortage  in  this 
element  is  very  unlikely.  It  seems  possible  from  recent  tests  that  sulfur  may  be  lacking  in 
many  soils,  for  applications  of  sulfur  fertilizers  have  proven  of  value  in  some  cases.  How- 
ever, little  is  known  as  yet  regarding  the  relation  of  this  element  to  soil  fertility.  If  later 
studies  show  its  importance  for  plant  growth  and  its  deficiency  in  soils,  sulfur  fertilizers  may 
come  to  be  considered  of  much  value. 

If  the  amounts  of  any  of  these  soil-derived  elements  in  soils  are  very  low,  they  need  to  be 
supplied  thru  fertilizers.  If  considerable  amounts  are  present,  fertilizers  containing  them  are 
unnecessary.  In  such  cases  if  the  mechanical  and  humus  conditions  in  the  soil  are  at  the  best, 
crops  will  be  able  to  secure  sufficient  food  from  the  store  in  the  soU.  For  example,  if  potas- 
sium is  abundant,  there  is  no  need  of  applying  a  potassium  fertilizer ;  if  phosphorus  is  deficient, 
a  phosphate  should  be  applied.  If  calcium  is  low  in  the  soil,  it  is  evident  that  the  soil  is  acid 
and  lime  should  be  applied,  not  ony  to  remedy  the  scarcity  of  calcium,  but  also  to  remedy  the 
injurious  acid  conditions. 

AVAILABLE  AND  UNAVAILABLE  PLANT  FOOD 

Frequently  a  soil  analysis  shows  the  presence  of  such  an  abundance  of  the  essential  plant 
foods  that  the  conclusion  might  be  drawn  that  crops  should  be  properly  supplied  for  an  in- 
definite period.  However,  application  of  a  fertilizer  containing  one  of  the  elements  present  in 
such  large  quantities  in  the  soil  may  bring  about  an  appreciable  and  even  profitable  increase 
in  crops. 

The  explanation  of  this  peculiar  state  of  affairs  lies  in  the  fact  that  all  the  plant  food 


POTTAWATTAMIE  COUNTY  SOILS  47 

shown  by  analysis  to  be  present  in  soils  is  not  in  a  usable  form;  it  is  said  to  be  unavailable. 
Plants  cannot  take  up  food  unless  it  is  in  solution;  hence  available  plant  food  is  that  which 
is  in  solution.  Analyses  show  not  only  this  soluble  or  available  portion  but  also  the  very  much 
larger  insoluble  or  unavailable  part.  The  total  amount  of  plant  food  in  the  soil  may,  tiiere- 
fore,  be  abundant  for  numerous  crops,  but  if  it  is  riot  made  available  rapidly  enough,  plants 
will  suffer  for  proper  food. 

Bacteria  and  molds  are  the  agents  which  bring  about  the  change  of  insoluble,  unavailable 
material  into  an  available  form.  If  conditions  in  the  soil  are  satisfactory  for  their  vigorous 
growth  and  sufficient  total  plant  food  is  present,  these  organisms  will  bring  about  the  produc- 
tion of  enough  soluble  material  to  support  good  crop  growth.  The  soil  conditions  necessary 
for  the  best  growth  and  action  of  bacteria  and  molds  are  the  same  as  those  which  are  required 
by  plants.  The  methods  necessary  to  maintain  permanent  soil  fertility  will,  therefore,  insure 
satisfactory  action  of  these  organisms  and  the  sufficient  production  of  available  plant  food. 
The  nitrogen  left  in  the  soil  in  plant  and  animal  remains  is  entirely  useless  to  plants  and  must 
be  changed  to  be  available.  Bacteria  bring  about  this  change  and  they  are  all  active  in  nor- 
mal soils  which  are  being  properly  handled. 

Phosphorus  is  found  in  soil  mainly  in  the  mineral  known  as  apatite  and  in  other  insoluble 
substances.  Potassium  occurs  chiefly  in  the  insoluble  feldspars.  Therefore,  both  of  these  ele- 
ments, as  they  normally  occur  in  soils,  are  unavailable.  However,  the  grovrth  of  bacteria  and 
molds  in  the  soil  brings  about  a  production  of  carbon  dioxide  and  organic  acids  which  act  on 
the  insoluble  phosphates  and  potassium  compounds  and  make  them  available  for  plant  food. 

Calcium  occurs  in  the  soil  mainly  in  an  unavailable  form,  but  the  compounds  containing  it 
are  attacked  by  the  soil  water  carrying  the  carbon  dioxide  produced  by  bacteria  and  molds 
and  as  a  result  a  soluble  compound  is  formed.  The  losses  of  lime  from  soils  are  largely  the 
result  of  the  leaching  of  this  soluble  compound. 

Sulfur,  like  nitrogen,  is  present  in  soils  chiefly  in  plant  and  animal  remains  in  which  form 
it  is  useless  to  plants.  As  these  materials  decompose,  however,  so-called  sulfur  bacteria  ap- 
pear and  bring  about  the  formation  of  soluble  and  available  sulfates. 

The  importance  of  bacterial  action  in  making  the  store  of  plant  food  in  the  soil  available  is 
apparent.  With  proper  physical  and  chemical  soil  conditions,  all  the  necessary  groups  of  bac- 
teria mentioned  become  active  and  a  vigorous  production  of  soluble  nitrogen,  phosphorus, 
potassium,  calcium  and  sulfur  results.  If  crops  are  to  be  properly  nourished  care  should  al- 
ways be  taken  that  the  soil  be  in  the  best  condition  for  the  growth  of  bacteria. 

EEMOVAL  OF  PLANT  FOOD  BY  CROPS 

The  decrease  of  plant  food  in  the  soil  is  the  direct  result  of  removal  by  crops,  although 
there  is  often  some  loss  by  leaching  also.  A  study  of  the  amounts  of  nitrogen,  phosphorus, 
and  potassium  removed  by  some  of  the  common  farm  crops  will  show  how  rapidly  these  ele- 
ments are  used  up  under  average  farming  conditions. 

The  amounts  of  these  elements  in  various  farm  crops  are  given  in  table  I.  The  amount  of 
calcium  and  sulfur  in  the  crops  is  not  included  as  it  is  only  recently  that  the  removal  of  these 
elements  has  been  considered  important  enough  to  warrant  analyses. 

The  figures  in  the  table  show  also  the  value  of  the  three  elements  contained  in  the  different 
crops,  calculated  from  the  market  value  of  fertilizers  containing  them.  Thus  the  value  of 
nitrogen  is  figured  at  16  cents  per  pound,  the  cost  of  the  element  in  nitrate  of  soda;  phos- 
phorus at  12  cents,  the  cost  in  acid  phosphate,  and  potassium  at  6  cents,  the  cost  in  muriate 
of  potash. 

It  is  evident  from  the  table  that  the  continuous  growing  of  any  common  farm  crop  without 
returning  these  three  important  elements  will  lead  finally  to  a  shortage  of  plant  food  in  the 
soil.  The  nitrogen  supply  is  drawn  on  the  most  heavily  by  all  the  crops,  but  in  the  case  of 
alfalfa  and  clover  only  a  small  part  should  be  taken  from  the  soil.  If  these  legumes  are  in- 
oculated as  they  should  be,  they  will  take  most  of  their  nitrogen  from  the  atmosphere.  The 
figures  are  therefore  entirely  too  high  for  the  nitrogen  taken  from  the  soil  by  these  two  crops, 
but  the  loss  of  nitrogen  from  the  soil  by  removal  in  non-leguminous  crops  is  considerable. 
The  phosphorus  and  potassium  in  the  soil  are  also  rapidly  reduced  by  the  growth  of  ordinary 
crops.  While  the  nitrogen  supply  may  be  kept  up  by  the  use  of  leguminous  green  manure 
crops,  phosphorus  and  potassium  must  be  supplied  by  the  use  of  expensive  commercial  fer- 
tilizers. 

The  cash  value  of  the  plant  food  removed  from  soils  by  the  growth  and  sale  of  various  crops 
is  considerable.  Even  where  the  grain  alone  is  sold  and  the  crop  residues  are  returned  to  the 
soil  there  is  a  large  loss  of  fertility,  and  if  the  entire  crop  is  removed  and  no  return  made,  the 


48 


SOIL  SURVEY  OF  IOWA 


TABLE  I.     PLANT  FOOD  IN  CROPS  AND  VALUE 

Calculating  Nitrogen  (N)  at  16c  (Sodium  Nitrate  (NaNOs)),  Phosphorus  (P)   at  12c  (Acid 
Phosphate),  and  Potassium  (K)    at  6c   (Potassium  Chloride   (KCl)) 


Yield 

Plant  Food,  Lbs. 

Value  of  Plant  Food 

Total 
Value 

Crop 

Nitrogen 

Phos- 
phorus 

Potassium 

Nitrogen 

Phos- 
phorus 

Potassium 

of 
Food 
Plant 

Corn,   grain 
Corn,  stover 
Corn   crop 
Wheat,  grain 
Wheat,    straw 
Wheat,   crop 
Oats,   grain 
Oats,  straw 
Oats  crop 
Barley  grain 
Barley    straw 
Barley  crop 
Rye   grain 
Rye   straw 
Rye  crop 
Potatoes 
Alfalfa  hay 
Timothy  hay 
Clover  hay 

75  bu. 
2.25  T. 

30  bu. 
1.5T. 

50  bu . 
1.25  T. 

30  bu. 

0.75  T. 

30'  bu." 
1.5T. 

300  bu. 
6T. 
3T. 
3T. 

75 

36 
111 

42.6 

15 

57.6 

33 

15.5 

48.5 

23 
9.5 

32.5 

29.4 

12 

41.4 

63 
300 

72 
120 

12.75 
4.5 

17.25 
7.2 
2.4 
9.6 
5.5 
2.5 
8 
5 
1 
6 
6 
3 
9 

12.7 

27 
9 

15 

14 
39 
53 

7.8 
27 
34.8 

8 
26 
34 

5.5 
13 
18.5 

7.8 
21 

28.8 
90 
144 
67.5 
90 

$12.00 

5.76 

17.76 

6.81 

2.40 

9.21 

5.28 

2.48 

7.76 

3.68 

1.52 

5.20 

4.70 

1.92 

6.62 

10.08 

48.00 

11.52 

19.20 

$1.53 
0.54 
2.07 
0.86 
0.28 
1.14 
0.66 
0.30 
0.96 
0.60 
0.12 
0.72 
0.72 
0.36 
1.08 
1.52 
3.24 
1.08 
1.80 

$0.84 
2.34 
3.18 
0.46 
1.62 
2.08 
0.48 
1.56 
2.04 
0.33 
0.78 
1.11 
0.46 
1.26 
1.72 
5.40 
8.64 
3.95 
5.40 

$14.37 

8.64 

23.01 

8.13 

4.30 

12.43 

6.42 

8.28 

14.70 

4.61 

2.42 

7.03 

5.88 

3.54 

9.42 

17.00 

59.88 

16.55 

16.40 

loss  is  almost  doubled.  It  is  evident,  therefore,  that  in  calculating  the  actual  income  from  the 
sale  of  farm  crops,  the  value  of  the  plant  food  removed  from  the  soil  should  be  subtracted 
from  the  proceeds,  at  least  in  the  case  of  constituents  which  must  be  replaced  at  the  present 
time. 

Of  course,  if  the  crops  produced  are  fed  on  the  farm  and  the  manure  is  carefully  preserved 
and  used,  a  large  part  of  the  valuable  matter  in  the  crops  will  be  returned  to  the  soil.  This 
is  the  case  in  livestock  and  dairy  farming  where  the  products  sold  contain  only  a  portion  of 
the  valuable  elements  of  plant  food  removed  from  the  soil.  In  grain  farming,  however,  green 
manure  crops  and  commercial  fertilizers  must  be  depended  upon  to  supply  plant  food  de- 
fiencies  in  the  soil.  It  should  be  mentioned  that  the  proper  use  of  crop  residues  in  this  latter 
system  of  farming  reduces  considerably  the  loss  of  plant  food. 

REMOVAL  PROM  IOWA   SOILS 

It  has  been  conservatively  estimated  that  the  plant  food  taken  from  Iowa  soils  and  shipped 
out  of  the  state  in  grain  amounts  to  about  $30,000,000  annually.  This  calculaion  is  based  on 
the  estimate  of  the  secretary  of  the  Western  Grain  Dealers'  Association  that  20  per  cent  of 
the  corn  and  35  to  40  per  cent  of  the  oats  produced  in  the  state  is  shipped  off  the  farms. 

This  loss  of  fertility  is  unevenly  distributed  over  the  state,  varying  as  farmers  do  more  or 
less  livestock  and  dairy  farming  or  grain  farming.  In  grain  farming,  where  no  manure  is 
produced  and  the  entire  grain  crop  is  sold,  the  soil  may  very  quickly  become  deficient  in  cer- 
tain necessary  plant  fo4pcls.  Eventually,  however,  all  soils  are  depleted  in  essential  food  mate- 
rials, whatever  system  of  farming  is  followed. 

This  loss  of  fertility  is  great  enough  to  demand  serious  attention.  Careful  consideration 
should  certainly  be  given  to  all  means  of  maintaining  the  soils  of  the  state  in  a  permanently 
fertile  condition. 

PERMANENT  FERTILITY  IN  IOWA  SOILS 

The  preliminary  study  of  Iowa  soils,  already  reported,*  revealed  the  fact  that  there  is  not 
an  inexhaustible  supply  of  nitrogen,  phosphorus  and  potassium  in  the  soils  of  the  state.  Po- 
tassium was  found  in  much  larger  amounts  than  the  other  two  elements,  and  it  was  concluded, 
therefore,  that  attention  should  be  centered  at  the  present  time  on  nitrogen  and  phosphorus. 
In  spite  of  the  fact  that  Iowa  soils  are  still  comparatively  fertile  and  crops  are  still  large, 

*  Bulletin  150  Iowa  Agricultural  Experiment  Station. 


POTTAWATTAMIE  CXDUNTY  SOILS  49 

there  is  abundant  evidence  at  hand  to  prove  that  the  best  possible  yields  of  certain  crops  are 
not  being  obtained  in  many  cases  because  of  the  lack  of  necessary  plant  foods  or  because  of 
the  lack  of  proper  conditions  in  the  soil  for  the  growth  of  plants  and  the  production,  by  bac- 
teria, of  available  plant  food. 

Proper  systems  of  farming  will  insure  the  production  of  satisfactory  crops  and  the  mainten- 
nance  of  permanent  fertility  and  the  adoption  of  such  systems  should  not  be  delayed  until 
crop  yields  are  much  lower,  for  then  it  will  involve  a  long,  tedious  and  very  expensive  fight  to 
bring  the  soil  back  to  a  fertile  condition.  If  proper  methods  are  put  into  operation  while 
comparatively  large  amounts  of  certain  plant  foods  are  still  present  in  the  soil,  it  is  relatively 
easy  to  keep  them  abundant  and  attention  may  be  centered  on  those  other  elements  which  are 
likely  to  be  limiting  factors  in  crop  production. 

Soils  may  be  kept  permanently  fertile  by  adopting  certain  practices  which  will  be  sum- 
marized here. 

CULTIVATION   AND   DEAINAGE 

Cultivation  and  drainage  are  two  of  the  most  important  farm  operations  in  keeping  the  soil 
in  a  favorable  condition  for  crop  production,  largely  because  they  help  to  control  the  moisture 
in  the  soil. 

The  moisture  in  soils  is  one  of  the  most  important  factors  governing  crop  production.  If 
the  soil  is  too  dry,  plants  suffer  for  a  lack  of  the  water  necessary  to  bring  them  their  food 
and  also  for  a  lack  of  available  plant  food.  Bacterial  activities  are  so  restricted  in  dry  soils 
that  the  production  of  available  plant  food  practically  ceases.  If  too  much  moisture  is 
present,  plants  likewise  refuse  to  grow  properly  because  of  the  exclusion  of  air  from  the  soil 
and  the  absence  of  available  food.  Decay  is  checked  in  the  absence  of  air,  all  beneficial  bac- 
terial action  is  limit-ed  and  humus,  or  organic  matter,  containing  plant  food  constituents  in 
an  unavailable  form,  accumulates.  The  infertility  of  low-lying,  swampy  soils  is  a  good  illus- 
tration of  the  action  of  excessive  moisture  in  restricting  plant  growth  by  stopping  aeration 
and  limiting  beneficial  decay  processes. 

While  the  amount  of  moisture  in  the  soil  depends  very  largely  on  the  rainfall,  any  excess 
of  water  may  be  removed  from  the  soil  by  drainage  and  the  amount  of  water  present  in  the 
soil  may  be  conserved  during  periods  of  drought  by  thoro  cultivation  or  the  maintaining  of  a 
good  mulch.  The  need  for  drainage  is  determined  partly  by  tlie  nature  of  the  soil,  but  more 
particularly  by  the  subsoil.  If  the  subsoil  is  a  heavy,  tight  clay,  a  surface  clay  loam  will  be 
rather  readily  affected  by  excessive  rainfall.  On  the  other  hand,  if  the  surface  soil  is  sandy,  a 
heavy  subsoil  will  be  of  advantage  in  preventing  the  rapid  drying  out  of  the  soil  and  also  in 
checking  losses  of  valuable  matter  by  leaching. 

Many  acres  of  land  in  the  Wisconsin  drift  area  in  Iowa  have  been  reclaimed  and  made 
fertile  thru  proper  drainage,  and  one  of  the  most  important  farming  operations  is  the  laying 
of  drains  to  insure  the  removal  of  excessive  moisture  in  heavy  soils. 

The  loss  of  moisture  by  evaporation  from  soils  during  periods  of  drought  may  be  checked 
to  a  considerable  extent  if  the  soil  is  cultivated  and  a  good  mulch  is  maintained.  Many 
pounds  of  valuable  water  are  thus  held  in  the  soil  and  a  satisfactory  crop  growth  secured  when 
otherwise  a  failure  would  occur.  Other  methods  of  soil  treatment,  such  as  liming,  green 
manuring  and  the  application  of  farm  manures,  are  also  important  in  increasing  the  water- 
holding  power  of  light  soils. 

THE  ROTATION  OF  OEOPS 

Experience  has  shown  many  times  that  the  continuous  growth  of  one  crop  takes  the  fer- 
tility out  of  a  soil  much  more  rapidly  than  a  rotation  of  crops.  One  of  the  most  important 
farm  practices,  therefore,  from  the  standpoint  of  soil  fertility,  is  the  rotation  of  crops  on  a 
basis  suited  to  the  soil,  climatic,  farm  and  market  conditions.  The  choice  of  crops  is  so  large 
that  no  diflieulty  should  be  experienced  in  selecting  those  suitable  for  all  conditions. 

Probably  the  chief  reason  wliy  the  rotation  of  crops  is  beneficial  may  be  found  in  the  fact 
that  different  crops  require  different  amount  of  the  various  plant  foods  in  the  soil.  One  par- 
ticular crop  will  remove  a  large  amount  of  one  element  and  the  next  crop,  if  it  be  the  same 
kind,  will  suffer  for  a  lack  of  tliat  element.  If  some  other  crop,  which  does  not  draw  as  heav- 
ily on  that  particular  plant  food,  is  rotated  with  the  former  crop,  a  balance  in  available  plant 
food  is  reached. 

Where  a  cultivated  crop  is  grown  continuously,  there  is  a  much  greater  loss  of  organic 
matter  or  humus  in  the  soil  than  under  a  rotation.  This  fact  suggests  a  second  explanation  for 
the  beneficial  effects  of  crop  rotations.  With  cultivation,  bacterial  action  is  much  increased 
and  the  humus  in  the  soil  may  be  decomposed  too  rapidly  and  the  soil  injured  by  the  removal 
of  the  valuable  material.     Then  the  production  of   available  plant  food  in   the  soil  will  bo 


50  SOIL  SUEVEY  OF  IOWA 

hindered  or  stopped  and  crops  may  suffer.  The  use  of  legumes  in  rotations  is  of  particular 
value  since  when  they  are  well  inoculated  and  turned  under  they  not  only  supply  organic  mat- 
ter to  the  soil,  but  they  also  increase  the  nitrogen  content. 

There  is  a  third  explanation  of  the  value  of  rotations.  It  is  claimed  that  crops  in  their 
growth  produce  certain  substances  called  "toxic"  which  are  injurious  to  the  same  crop,  but 
have  no  effect  on  certain  otlier  crops.  In  a  proper  rotation  the  time  between  two  different 
crops  of  the  same  plant  is  long  enough  to  allow  the  "toxic"  substance  to  be  disposed  of  in  the 
soil  or  made  harmless.  This  theory  has  not  been  commonly  accepted,  chiefly  because  of  the 
lack  of  confirmatory  evidence.  It  seems  extremely  doubtful  if  the  amounts  of  these  "toxic" 
substances  could  be  large  enough  to  bring  about  the  effects  evidenced  in  continuous  cropping. 

But,  whatever  the  reason  for  the  bad  effects  of  continuous  cropping,  it  is  evident  that  for 
all  good  systems  of  farming  some  definite  rotation  should  be  adopted,  and  that  rotation  should 
contain  a  legume,  because  of  the  value  of  such  crops  to  the  soil.  In  no  other  way  can  the 
humus  and  nitrogen  content  of  soils  be  kept  up  so  cheaply  and  satisfactorily  as  by  the  use 
of  legumes,  either  as  regular  or  "catch"  crops  in  the  rotation. 

MANUEING 

There  must  always  be  enough  humus,  or  organic  matter,  and  nitrogen  in  the  soil  if  satis- 
factory crops  are  to  be  secured.  Humus  not  only  keeps  the  soil  in  the  best  physical  condition 
for  crop  growth,  but  it  supplies  a  considerable  portion  of  nitrogen.  An  abundance  of  humus 
may  always  be  considered  a  reliable  indication  of  the  presence  of  much  nitrogen.  This  nitro- 
gen does  not  occur  in  a  form  available  for  plants,  but  with  proper  physical  conditions  in  the 
soil,  the  nonusable  nitrogen  in  the  animal  and  vegetable  matter  which  makes  up  the  humus, 
is  made  usable  by  numerous  bacteria  and  changed  into  soluble  and  available  nitrates. 

The  humus,  or  organic  matter,  also  encourages  the  activities  of  many  other  bacteria  which 
produce  carbon  dioxide  and  various  acids  which  dissolve  and  make  available  the  insoluble  phos- 
phorus and  potassium  in  the  soil. 

Three  materials  may  be  used  to  supply  the  organic  matter  and  nitrogen  of  soils.  These  are 
farm  manure,  crop  residues  and  green  manure,  the  first  two  being  much  more  common. 

Farm  manure  is  composed  of  the  solid  and  liquid  excreta  of  animals,  litter,  unconsumed 
food  and  other  waste  materials,  and  supplies  an  abundance  of  organic  matter,  much  nitrogen 
and  millions  of  valuable  bacteria.  It  contains,  in  short,  a  portion  of  the  plant  food  present 
in  the  crops  originally  removed  from  the  soil  and  in  addition  the  bacteria  necessary  to  prepare 
this  food  for  plant  use.  If  it  were  possible  to  apply  large  enough  amounts  of  farm  manure, 
no  other  material  would  be  necessary  to  keep  the  soil  in  the  best  physical  condition,  insure 
efiicient  bacterial  action  and  keep  up  the  plant  food  supply.  But  manure  cannot  serve  the 
soil  thus  efficiently,  for  even  under  the  very  best  methods  of  treatment  and  storage,  15  per 
cent  of  its  valuable  constituents,  mainly  nitrogen,  are  lost.  Furthermore,  only  in  a  very  few 
instances  is  enough  produced  on  a  farm  to  supply  its  needs.  On  practically  all  soils,  there- 
fore, some  other  material  must  be  applied  with  the  manure  to  maintain  fertility. 

Crop  residues,  consisting  of  straw,  stover,  roots  and  stubble,  are  important  in  keeping  up 
the  humus,  or  organic  matter  content  of  soils.  Table  I  shows  that  a  considerable  portion  of 
the  plant  food  removed  by  crops  is  contained  in  the  straw  and  stover.  On  all  farms,  therefore, 
and  especially  on  grain  farms,  the  crop  residues  should  be  returned  to  the  soil  to  reduce  the 
losses  of  plant  food  and  also  to  aid  in  maintaining  the  humus  content.  These  materials  alone 
are,  of  course,  insufficient  and  farm  manure  must  be  used  when  possible,  and  green  manures 
also. 

Green  manuring  should  be  followed  to  supplement  the  use  of  farm  manures  and  crop  resi- 
dues. In  grain  farming,  where  little  or  no  manure  is  produced,  the  turning  under  of  legumin- 
ous crops  for  green  manures  must  be  relied  upon  as  the  best  means  of  adding  humus  and 
nitrogen  to  the  soil,  but  in  all  other  systems  of  farming  also  it  has  an  important  place.  A 
large  number  of  legumes  will  serve  as  green  manure  crops  and  it  is  possible  to  introduce  some 
such  crop  into  almost  any  rotation  without  interfering  with  the  regular  crop.  It  is  this  pecu- 
liarity of  legumes,  together  with  their  ability  to  use  the  nitrogen  of  the  atmosphere  when  well 
inoculated,  and  thus  increase  the  nitrogen  content  of  the  soil,  which  gives  tliom  their  great 
value  as  green  manure  crops. 

It  is  essential  that  the  legumes  used  be  well  inoculated.  Their  ability  to  use  the  atmos- 
pheric nitrogen  depends  on  that.  Inoculation  may  be  accomplished  by  the  use  of  soil  from  a 
field  where  the  legume  has  previously  been  successfully  grown  and  well  inoculated,  or  by  the 
use  of  inoculating  material  that  may  be  purchased.  If  the  legume  has  never  been  grown  on 
the  soil  before,  or  has  been  grown  without  inoculation,  then  inoculation  should  be  practiced 
by  one  of  these  methods. 


POTTAWATTAMIE  COUNTY  SOILS  51 

By  using  aU  the  crop  residues,  all  the  manure  produced  on  the  farm,  and  giving  well  in- 
oculated legumes  a  place  in  the  rotation  for  green  manure  crops,  no  artificial  means  of  main- 
taining the  humus  and  nitrogen  content  of  soils  need  be  resorted  to. 

THE  USE  OF  PHOSPHORUS 

Iowa  soils  are  not  abundantly  supplied  with  phosphorus.  Moreover,  it  is  impossible  by  the 
use  of  manures,  green  manures,  crop  residues,  straw,  stover,  etc.,  to  return  to  the  soil  the  en- 
tire amount  of  that  element  removed  by  crops.  Crop  residues,  stover  and  straw  merely  re- 
turn a  portion  of  the  phosphorus  removed,  and  while  their  use  is  important  in  checking  the 
loss  of  the  element,  they  cannot  stop  it.  Green  manuring  adds  no  phosphorus  that  was  not 
used  in  the  growth  of  the  green  manure  crop.  Farm  manure  returns  part  of  the  phosphorus 
removed  by  crops  which  are  fed  on  the  farm,  but  not  all  of  it.  While,  therefore,  immediate 
scarcity  of  phosphorus  in  Iowa  soils  cannot  be  positively  shown,  analyses  and  results  of  ex- 
periments show  that  in  the  more  or  less  distant  future,  phosphorus  must  be  applied  or  crops 
will  suffer  for  a  lack  of  this  element.  Furthermore,  there  are  indications  that  its  use  at 
present  would  prove  profitable  in  some  instances. 

Phosphorus  may  be  applied  to  soUs  in  three  commercial  forms,  bone  meal,  acid  phosphate 
and  rock  phosphate.  Bone  meal  cannot  be  used  generally,  because  of  its  extremely  limited 
production,  so  the  choice  rests  between  rock  phosphate  and  acid  phosphate.  Experiments  are 
now  under  way  to  show  which  is  more  economical  for  all  farmers  in  the  state.  Many  tests 
must  be  conducted  on  a  large  variety  of  soil  types,  under  widely  differing  conditions,  and 
thru  a  rather  long  period  of  years.  It  is  at  present  impossible  to  make  these  experiments  as 
complete  as  desirable,  owing  to  small  appropriations  for  such  work,  but  the  results  secured 
from  the  tests  now  in  progi-ess  will  be  published  from  time  to  time  in  the  different  county  re- 
ports. 

Until  such  definite  advice  can  be  given  for  individual  soil  types,  it  is  urged  that  farmers 
who  are  interested  make  comparisons  of  rock  phosphate  and  acid  phosphate  on  their  own 
farms.  In  this  way  they  can  determine  at  first  hand  the  relative  value  of  the  two  materials. 
Information  and  suggestions  regarding  the  carrying  out  of  such  t«sts  may  be  secured  upon 
application  to  the  Soils  Section. 

LIMING 

Practically  all  crops  grow  better  on  a  soil  which  contains  lime,  or  in  other  words,  on  one 
which  is  not  acid.  As  soils  become  acid,  crops  grow  smaller,  bacterial  activities  are  reduced 
and  the  soil  becomes  infertile.  Crops  are  differently  affected  by  acidity  in  the  soil;  some 
refuse  to  grow  at  all;  others  grow  but  poorly.  Only  in  a  very  few  instances  can  a  satisfactory 
crop  be  secured  in  the  absence  of  lime.  Therefore,  the  addition  of  lime  to  soils  in  which  it  is 
lacking  is  an  important  principle  in  permanent  soil  fertility.  All  soils  gradually  become  acid 
because  of  the  losses  of  lime  and  other  basic  materials  thru  leaching  and  the  production  of 
acids  in  the  decomposition  processes  constantly  occurring  in  soils.  Iowa  soils  are  no  excep- 
tion to  the  general  rule,  as  was  shown  by  the  tests  of  many  representative  soils  reported  in 
bulletin  No.  151  of  this  Station.  Particularly  are  the  soils  in  the  lowan  drift,  Mississippi 
loess  and  Southern  Iowa  loess  areas  likely  to  he  acid. 

All  Iowa  soils  should  therefore  be  tested  for  acidity  before  the  crop  is  seeded,  particularly 
when  legumes,  such  as  alfafa  or  red  clover,  are  to  be  grown.  Any  farmei*  may  test  his  own 
soil  and  determine  its  need  of  lime,  according  to  simple  directions  given  in  bulletin  151,  re- 
ferred to  above. 

As  to  the  amount  of  lime  needed  for  acid  soils  as  a  general  rule  sufficient  should  be  applied 
to  neutralize  the  acidity  in  the  surface  soil  and  then  an  additional  amount  of  one  to  two  tons 
per  acre. 

SOIL  AREAS  IN  IOWA 

There  are  five  large  soil  areas  in  Iowa,  the  Wisconsin  drift,  the  lowan  drift,  the  Missouri 
loess,  the  Mississippi  loess  and  the  Southern  Iowa  loess.  These  five  divisions  of  the  soils  of 
the  state  are  based  on  the  geological  forces  which  brought  about  the  formation  of  the  various 
soil  areas.     The  various  areas  are  shown  in  the  accompanying  map. 

With  the  exception  of  the  northeastern  part  of  the  state,  the  whole  surface  of  Iowa  was 
in  ages  past  overrun  by  great  continental  ice  sheets.  These  great  masses  of  ice  moved  slowly 
over  the  land,  crushing  and  grinding  the  rocks  beneath  and  carrying  along  with  them  the 
material  which  they  accumulated  in  their  progress.  Five  ice  sheets  invaded  Iowa  at  different 
geological  eras,  coming  from  different  directions  and  carrying,  therefore,  different  rock  mate- 
rial with  them. 


52 


SOIL  SUEVEY  OF  IOWA 


The  deposit,  or  sheet,  of  earth  debris  left  after  the  ice  of  such  glaciers  melts  is  called 
"glacial  till"  or  "drift"  and  is  easily  distinguished  by  the  fact  that  it  is  usually  a  rather 
stiff  clay  containing  pebbles  of  all  sorts  as  well  as  large  boulders  or  "nigger-heads."  Two 
of  these  drift  areas  occur  in  Iowa  to-day,  the  Wisconsin  drift  and  the  lowan  drift,  covering 
the  north  central  part  of  the  state.  The  soils  of  these  two  drift  areas  are  quite  different  in 
chemical  composition,  due  primarily  to  the  different  ages  of  the  two  ice  invasions.  The  lowan 
drift  soil  was  laid  down  at  a  much  earlier  period  and  is  somewhat  poorer  in  plant  food  than 
the  Wisconsin  drift  soil,  having  undergone  considerable  leaching  action  in  tlie  time  which  has 
elapsed  since  its  formation. 

The  drift  deposits  in  the  remainder  of  the  state  have  been  covered  by  so-called  loess  soils, 
vast  accumulations  of  dust-like  materials  which  settled  out  of  the  air  during  a  period  of 
geological  time  when  climatic  conditions  were  very  different  than  at  present.  These  loess 
soils  are  very  porous  in  spite  of  their  fine  texture  and  they  rarely  contain  large  pebbles  or 
stones.  They  present  a  strong  contrast  to  the  drift  soils,  which  are  somewhat  heavy  in  texture 
and  filled  with  pebbles  and  stones.  The  three  loess  areas  in  the  state,  the  Missouri,  the  Mis- 
sissippi and  the  Southern  Iowa,  are  distinguished  by  differences  in  texture  and  appearance, 
and  they  vary  considerably  in  value  for  farming  purposes.  In  some  sections  the  loess  is  very 
deep,  while  in  other  places  the  underlying  leached  till  or  drift  soil  is  very  close  to  the  surface. 
The  fertility  of  these  soils  and  their  needs  are  greatly  influenced,  therefore,  by  their  depth. 

It  will  be  seen  that  the  soils  of  the  state  may  be  roughly  divided  into  two  classes,  drift 
soils  and  loess  soils,  and  that  further  divisions  may  then  be  made  into  various  drift  and  loess 
soils  because  of  differences  in  period  of  formation,  characteristics  and  general  composition. 
More  accurate  information  demands,  however,  that  further  divisions  be  made.  The  different 
drift  and  loess  soils  contain  large  numbers  of  soil  types  which  vary  among  themselves,  and 
each  of  these  should  receive  special  attention. 

THE  SOIL  SURVEY  BY  COUNTIES 

It  is  apparent  that  a  general  survey  of  the  soils  of  the  state  can  gfve  only  a  very  general 
idea  of  soil  conditions.  Soils  vary  so  widely  in  character  and  composition,  depending  on  many 
other  factors  than  their  source,  that  definite  knowledge  concerning  their  needs  can  be  secured 
only  by  thoro  and  complete  study  of  them  in  place  in  small  areas.     The  climatic  conditions, 


Fig.  11.     Map  showing  the  principal  soil  areas  in  Iowa 


POTTAWATTAMIP]  COUNTY  SOILS  53 

topograjiliy,  depth  and  cliaiJU't^r  of  tlie  soil,  cheinieal  and  mechanical  composition,  and  in  short 
all  the  factors  which  may  affect  crop  production,  must  be  considered. 

This  is  what  is  accomplished  by  the  soil  survey  of  the  state  by  counties,  and  hence  the 
needs  of  individual  soils,  and  proper  systems  of  management  may  be  worked  out  in  much 
greater  detail  and  be  much  more  complete  than  would  V)e  possiVde  by  merely  considering  the 
large  soil  areas  separated  on  tlie  basis  of  their  geological  origin.  In  other  words,  while  the 
unit  in  tlie  general  survey  is  the  geological  history  of  the  soil  area,  in  the  soil  survey  by  coun- 
ties or  any  other  small  area,  the  unit  is  the  soil  type. 

GENERAL  SOIL  CHARACTERISTICS 

Soil  types  possess  more  or  less  definite  characteristics  which  may  be  determined  largely  in 
the  field,  altho  some  laboratoiy  study  is  necessary  for  final  disi)Osition.  Usually  the  line  of 
separation  Vjetween  adjoining  soil  types  is  quite  distinct  and  it  is  a  simple  matter  to  locate 
tlie  type  Ixjundaries.  In  some  cases,  however,  there  is  a  gradation  from  one  type  to  another 
and  then  tiie  boundaries  may  be  fixed  only  with  great  difficulty.  The  error  introduced  into 
the  soil  sui-\'ey  work  from  this  souicc  is  very  small  and  need  cause  little  concern. 

The  factors  which  must  be  tjikeii  into  account  in  establishing  soil  types  have  Ih'cu  well 
enumerated  by  tlie  Illinois  Agricultural  Experiment  Station  in  its  Soil  Report  No.  1.     They  are: 

1.  The  geological  origin  of  the  soil,  whether  residual,  glacial,  loessial,  alluvial,  colluvial  or 
cumulose. 

2.  The  topography  or  lay  of  the  land. 

.'5.     The  structure  or  depth  anil  character  of  the  surface,  subsurface  and  subsoil. 

4.  The  physical  or  mechanical  composition  of  different  strata  composing  the  soil,  as  the 
jiercentages  of  gravel,  sand,  silt,  clay  and  organic  matter  which  they  contain. 

5.  The  texture  or  porosity,  granulation,  friability,  plasticity,  etc. 

6.  The  color  of  the  strata. 

7.  The  natural  drainage. 

8.  The  agricultural  value  based  upon  its  natural  productiveness. 

9.  Native  vegetation. 

10.  The  ultimate  chemical  composition  and  reaction. 

The  common  soil  constituents  may  be  given  as  follows  i  according  to  the  Bureau  of  Soils: 

Organic  Matter    \  ^^^  Partially  destroyed  or  undecomposed 
/      vegetable  and  animal  material. 

Stones — over  32  mm.* 
Gravel— 32— 2.0    mm. 
Very  coarse  sand 
Coarse  Sand — -1.0 — 0..5  mm. 
Medium   Sand — 0..5 — 0.2.5   mm. 
Fine  Sand— 0.25— 0.10  mm. 
Very  fine  Sand — 0.10 — 0.0,5  mm. 
Silt— 0.05— 0.00   mm. 

SOILS  GROUPED  BY  TYPES 

The  different  geueral  groujjs  of  soils  by  types  are  indicated  thus  by  the  Bureau  of  soils: 2 

Peats — Consisting  of  35  per  cent  or  more  of  organic  matter,  sometimes  mixed  with  more 
or  less  sand  or  soil. 

Peaty  Loams — 15  to  35  per  cent  of  organic  matter  mixed  with  much  sand  and  silt  and  a 
little  clay. 

Muds — 25  to  35  per  cent  of  partly  decomposed  organic  matter  mixed  with  much  clay  and 
some  silt. 

Clays — Soils  with  more  than  30  per  cent  clay,  usually  mixed  with  much  silt ;  always  more 
than  50  per  cent  silt  and  clay. 

Silty  Clay  Loams — 20  to  30  per  cent  clay  and  more  than  50  per  cent  silt. 

Clay  Loams — 20  to  30  per  cent  clay  and  less  than  50  per  cent  silt  and  some  sand. 

Silt  Loams — 20  per  cent  clay  and  more  than  50  per  cent  silt  mixed  with  some  sand. 

Loams — Less  than  20  per  cent  clay  and  less  than  50  per  cent  silt  and  from  30  to  50  per 
cent   sand. 

*  25  mm.  equals  1  in. 

1  Bur.  of  Soils  Field  Book. 

2  1  C. 


Inorganic  Matter 


54  SOIL  SURVEY  OF  IOWA 

Sandy  Clays — 120  i>er  cent  silt  and  snnill  amounts  of  clay  up  to  30  i)er  cent. 

Fine  Sandy  Loams — More  than  50  ])er  cent  fine  sand  and  very  fine  sand  mixed  with  less  than 
25  per  cent  very  coarse  sand,  coarse  sand  and  medium  stind,  much  silt  and  a  little  clay;  silt 
and  clay  20  to  50  per  cent. 

Sandy  Loams — More  than  25  per  cent  very  coarse,  coarse  and  medium  sand;  silt  and 
clay  20  to   50  per  cent. 

Very  Fine  Sand — More  tiiaai  50  per  cent  fine  siind  ;ind  less  than  25  per  cent  very  coarse, 
coarse  and  medium  sand,  less  than  20  per  cent  silt  and  clay. 

Fine  Sand — More  than  50  per  cent  fine  sand  and  less  than  25  per  cent  very  coarse,  coarse 
and  medium  sand,  less  than  20  per  cent  silt  and  clay: 

Sand — More  than  25  per  cent  very  coarse,  coarse  and  medium  sand,  less  than  50  per  cent  fine 
sand,  less  than  20  per  cent  silt  and  clay. 

Coarse  Sand — More  than  25  {ht  cent  very  coarse,  coarse  an<l  medium  sand,  less  than  50  per 
cent  of  other  grades,  less  than  20  per  cent  silt  and  clay. 

Crravelly  Loams — 25  to  50  j)er  c^nt  very  coarse  sand  and  much  sand  and  some  silt. 

Gravels — More  than  50  per  cent  very  coarse  sand. 

Stony  Loams — A  large  number  of  stones  over  one  inch  in  diameter. 

METHOD  USED  IN  THE  SOIL  SUBVEY 

It  may  be  of  some  interest  to  state  briefly  the  methods  wliich  are  followed  in  the  field  in 
surveying  soils. 

As  has  been  indicated,  the  completed  map  is  intended  to  show  the  accurate  location  and 
boundaries,  not  only  of  all  the  soil  types  but  also  of  the  streams,  roads,  railroads,  etc. 

The  first  step,  therefore,  is  the  choice  of  an  accurate  base  map  and  any  oflScial  map  of  the 
county  may  he  chosen  for  this  purpose.  Such  maps  are  always  checked  to  correspond  cor- 
rectly with  the  land  survey.  The  location  of  every  stream,  road  and  railroad  on  the  map 
is  likewise  carefully  verified  and  corrections  are  frequently  necessary.  When  an  accurate 
base  map  is  not  available  it  is  the  first  duty  of  the  field  party  to  prepare  one. 

The  section  is  the  unit  area  by  which  each  county  is  surveyed  and  mapped.  The  distances 
in  the  roads  are  determined  by  an  odometer  attached  to  the  vehicle,  and  in  the  field  by  pacing, 
which  is  done  with  accuracy.  The  directions  of  the  streams,  roads,  raUroads,  etc.,  are  deter- 
mined by  the  use  of  the  compass  and  the  plane  table.  The  character  of  the  soil  types  is  as- 
certained in  the  section  by  the  use  of  the  auger,  an  instrument  for  sampling  both  the  surface 
soil  and  the  subsoil.  The  boundaries  of  each  type  are  then  ascertained  accurately  in  the  sec- 
tion and  indicated  on  the  map.  Many  samplings  are  frequently  necessaiy,  and  individual 
sections  may  contain  several  soil  types  and  require  much  time  for  mapping.  In  other  cases, 
the  entire  section  may  contain  only  one  soil  type,  which  fact  is  readily  ascertained,  and  in 
that  case  the  mapping  may  proceed  rapidly. 

When  one  section  is  completed,  the  party  passes  to  the  next  section  and  the  location  of  all 
soil  tyjies,  streams,  ete.,  in  that  section  is  then  checked  with  their  location  in  the  adjoining 
area  just  mapped.  Careful  attention  is  paid  to  the  topographic  features  of  the  area,  or  the 
"lay  of  the  land,"  for  the  character  of  the  soils  is  found  to  correspond  very  closely  to  the 
conditions  under  which  they  occur. 

The  field  party  is  composed  of  two  men,  and  all  observations,  measurements  and  soil  type 
boundaries  are  compared  and  checked  by  each  man. 

The  determinations  of  soil  types  are  verified  also  by  inspection  by  and  .'consultation  with 
those  in  charge  of  the  work  at  the  Bureau  of  Soils  and  at  the  Iowa  Agricultural  Experiment 
Station.  When  the  entire  county  is  completed,  all  the  section  maps  or  field  sheets  are  as- 
sembled and  any  variations  or  questionalde  boundaries  are  verified  by  further  observations 
of  the  particular  area. 

The  completed  map,  therefore,  shows  as  accurately  as  possible  all  soils  and  soil  boundaries, 
and  it  constitutes  also  an  exact  road  map  of  the  county. 


UC  SOUTHERN  REGIONAL  LIBRARY  FACILITY 


D  000  986  901 


